Fanon VS Canon
Harry is always sweet and kindly.
JK Rowling has said in interview that Harry would never fail to help someone in pain, and that his encounter with the fragment of Voldemort's soul at King's Cross was the first time he had felt revulsion for suffering rather than wanting to help. This is one of those cases where an interview cannot be accepted as canon because it clearly clashes with what's in the books.
It's true Harry is quite often kind when he remembers to be - but he often forgets. In the first book canon Harry is amused by Dudley's pain and fear when Hagrid attacks him, and eats in front of the Dursleys when they must be ravenously hungry, although they had shared their meagre rations of the night before equally with him (not that this last is really Harry's fault, since Vernon instructs Dudley and Petunia not to eat Hagrid's food - probably a wise move when it comes to the sausages). He has to be dragged away from a book on nasty magical things you can do to your enemies. In CoS he chooses to kill the basilisk in a very cruel way without even trying to talk to her and persuade her to change sides, although they share a language. In PoA he gloats over the idea of sending Sirius back to the Dementors when he believes he is guilty; he looks at Snape lying unconscious and bleeding after Snape has rushed into danger to protect him, and wonders if he is dead, but doesn't care; and he is either neutral towards or actively amused by Sirius's rough treatment of the still unconscious Snape.
In GoF he is amused to see ferret!Draco being repeatedly battered against a stone floor as he screams in pain; is unconcerned by the agony of the Crucioed spider; and has no problem with Hermione kidnapping a woman and holding her prisoner for weeks, apparently without even telling her family that she's all right. In OotP he deliberately supresses information which could have helped in the treatment of Montague, although Montague is so badly injured that weeks later he is still being spoon-fed in the hospital wing; is unconcerned by the fact that adult Snape is clearly traumatised by the Pensieve incident (even though he does care about teen-Snape); and has no problem with badly scarring a young girl's face for life to punish her for being more loyal to her mother than to a friend of a friend she barely knows. In HBP he practises hexes on a Squib, and in DH he tortures somebody and throws him through a glass door just for being rude, and is revolted by Aberforth's ancient misery. Twice he leaves Draco, Crabbe and Goyle to spend an eight-hour train journey contorted beyond recognition by what are probably very painful hex injuries, without (so far as we know) even a drink of water or a lavatory break, and has no problem with seeing the Twins deliberately tread on them as they lie injured and helpless.
[SPOILER for The Cuckoo's Calling: Harry's cold revulsion at Aberforth's unhappiness is probably some characteristic of JK herself, as she has her detective Cormoran Strike behave the same way. He is repelled by the tears of a mother who has just learned that one of her children has killed the other two, and is coldly impatient with her grief.]
We see Harry at his best, perhaps, when he feels acute sorrow for the way Luna is isolated and persecuted (even though it seems to bother him more than it does her), and when he is deeply upset to see that his father and Sirius really were bullies who persecuted schoolboy Snape; when he kneels quietly by the dying Snape and accepts his memories, even though he still believes him to be an enemy; when he saves Draco and Goyle from the consequences of Crabbe's stupidity; when he is tolerant of Kreacher even though he knows Kreacher betrayed Sirius to his death. His behaviour towards oddball Luna stands in sharp contrast with his father's behaviour to oddball Snape, and he even wants to help the unpopular Mrs Norris when she is frozen by the Basilisk, although he seems to be about to let Ron talk him out of it.
We see him at his worst when he sees Snape lying unconscious and bleeding in the Shrieking Shack in PoA, wonders if he is dead but does nothing about it; when he seems quite amused to see Sirius brutalising the unconscious Snape and banging his head against the ceiling; when he initially approves of prisoners in Azkaban being tormented by Dementors (in contrast with Remus's dislike of the idea) and likes the idea of sending Sirius - who at that point he believes to be guilty - to suffer; when he practises hexes on a Squib; when he leaves the magically-distorted Draco, Crabbe and Goyle to suffer for a whole eight-hour train journey, twice, without water or a lavatory break; when he talks Hermione out of doing anything to help Montague after the Twins have seriously injured him; when he is quite unconcerned about false!Moody torturing an experimental animal with Cruciatus; when he himself tortures an enemy just for being rude. The situation is complicated, of course, by the fact that some of Harry's worst behaviour may be being caused by proximity to the chunk of Voldemort which is stuck to his forehead.
Harry is in some ways rather cold, without that much inner life. Really, this is because he is the viewpoint character and Rowling doesn't always fill in what he is thinking and feeling, as opposed to what he is witnessing, but it leaves his emotional life seeming a bit flat. That he actually is a bit cold is shown in the scene in DH just after they have escaped from the raid on the Weasley wedding, and Arthur's Patronus comes to them at Grimmauld Place to tell them that the family have survived. Ron and Hermione are both almost hysterical with relief on learning that the Weasleys are OK, even though Molly hasn't always treated Hermione well. Harry has to consciously think about Ginny before he can share their relief. Molly and Arthur love him, they treat him in some ways better than their own sons, but their fate does not engage him. In fact he explicitly says that he would have been equally as relieved as Ron and Hermione if the Weasleys had been his own family (i.e., because they aren't, he isn't) - "'It's your family, 'course you're worried. I'd feel the same way.' He thought of Ginny. 'I do feel the same way.'" The lack of a blood connection had not stopped Hermione from being as relieved as Ron, but Harry only has strong emotion about Ginny.
Harry's background and character have been very carefully constructed. Had the Dursleys been his actual parents, and treated him as they do, he would probably have grown up with very low self-esteem, feeling that he must be a horrible person if the people who were meant to love him in fact barely tolerated him. But he knows they're not his parents, that his parents probably did love him, and the Dursleys have made it plain that he was imposed on them against their will, so he doesn't have to feel that they ought to love him and that there's something wrong with him if they don't.
If the Dursleys had been physically or sexually abusive Harry might have grown up nervous and meek, trying to placate them so they wouldn't hurt him, or have ended up as jumpy and snarly as a stray cat, the way Snape is. If they had sometimes shown him love then he would have become needy and anxious in the hopes of getting more. But since they were always cold but never especially threatening they were just an unpleasant background noise which would be upsetting if he allowed himself to notice and care about it, but which he could quite easily tune out. Hence he grew up extremely self-contained and with no desire to win adult approval, and with not much awareness of adults as thinking, feeling people like himself. And because they punished him for magical accidents which he couldn't help and didn't even know if he'd done, but don't seem to punish him for things which he can help (such as being cheeky), he treats punishment as a random irritant, like bad weather, which has nothing to do with his own behaviour. He loves McGonagall, as much as he does any adult aside from Sirius and Hagrid, but the idea that if she's giving him yet another detention she must be displeased with him and that maybe, just maybe, he might consider changing his behaviour, or that his ignoring her wishes might cause her pain, never seems to occur to him.
This probably contributes to his poor relationship with Snape. Snape has a very exaggerated idea of how much Harry desires fame (which isn't zero, because he likes being praised for doing well at sports), but that aside, the things he nags Harry about are things he really thinks Harry could and should do better in class - beginning with putting Harry on the spot in their first lesson and trying to get him to think about potions, after catching Harry communicating with Ron instead of paying attention to the teacher, just after he has made his big keynote speech. But Harry really doesn't associate adult anger with his own behaviour. If he never thinks "If McGonagall is giving me detention for doing X, maybe I should stop doing it", he's certainly never going to think "If Snape is snarling at me for doing Y, maybe I should stop doing it." Snape doesn't know about Uncle Vernon and doesn't know that Harry screens out adult anger as so much white noise, and needs to be cajoled - and even if he did understand it he may not know how to do it.
Prior to the final battle Harry hates Snape, at times understandably because Snape has done something offensive, but at times in a deranged, obsessive way where everything about Snape, his voice, his manner, his appearance strikes Harry as some sort of crime and he fantasizes about torturing him, even when he knows Snape has made sacrifices to protect him. He also fantasized about sending Sirius back to the Dementors and wanted him to suffer, before he found out that he was innocent, and then later he blames Snape for Sirus's death to an irrational degree. This exaggerated hatred of Snape may in part be because he, or the Horcrux, senses the presence of the Dark Mark but it's also possible that it's a safety valve.
The key, I think, is that Harry thinks he wants Sirius to suffer and die for betraying his parents, but when he is confronted with the terrified, grovelling reality of Peter Pettigrew, the man who really did betray his parents and who is right there in his power, waiting for execution, he spares him. When he has Kreacher in his power, Kreacher who has to do absolutely anything Harry tells him to, Kreacher who really did betray Sirius to his death, Harry is no worse than a bit abrupt with him (much like Snape, who does nothing worse to Pettigrew, his childhood bully who betrayed Lily to her death, than boss him about and make him do a little house-work). When he is personally responsible for dealing with a helpless, dying Snape he is suddenly polite and obliging, even though as far as he knows at that point, Snape is an enemy.
It looks as though he hates Snape, prior to the death scene, in part because Snape is a safe person to hate. If he lets his justified rage against the Dursleys or against Kreacher rise up, he could really hurt them, either through subconscious, wandless magic or deliberately; but he can project all his rage at Vernon onto Snape and Snape will brush it off with a sneer, because he's a strong adult wizard and it's unlikely Harry can do him much damage. In fact, then, most of the time Harry doesn't really want to hurt anybody. He thinks he does, but when he has the chance to take real revenge on someone who really has performed a great crime against Harry or his nearest and dearest, and who can't defend themselves, he does them a good turn.
He is, of course, very cold and callous towards the injured, unconscious Snape in the Shrieking Shack - he sees the man lying there bleeding and wonders if he is dead, but does nothing about it. He watches Sirius letting Snape's head bang against the ceiling, and either approves or doesn't dissapprove enough to say anything. But at this point he has suffered so many emotional reverses in such a short period of time that he may be suffering from psychological shock, and he is not himself responsible for Sirius's brutality. Like Remus with James and Sirius, Severus with Mulciber, Harry is willing to go along with violence committed by Sirius, Hagrid and the Twins because they are friends of his, even when he wouldn't be violent in that way himself.
This relative gentleness begins to change, though, from HBP onwards, perhaps because Harry is warping with age or with exposure to wizard culture, or perhaps because of increasing pressure on his mind from Voldemort. During HBP he enjoys practising the Half-Blood Prince's hexes on Filch, a Squib. OK, aside from Sectumsempra the Prince's spells seem to be fairly harmless, and Filch is a creepy old perv who wants to torture the students (or says he does) - but practising spells on somebody who can't fight back is dishonourable and shows Harry beginning to turn into a bully.
In DH he uses Imperius freely - and he has sound military reasons to do so, but one would like to see him at least hesitate. Much worse, although he has been Cruciated himself and knows how horrible it is, he Cruciates Amycus just for spitting at McGonagall, and throws him into a sheet of glass which may well have seriously injured him. All just for being rude, and it wasn't even a good move militarily - it would have been far safer and more reliable just to Stupefy Amycus from behind - under cover of the Cloak, if it's possible to cast spells from under it, or if not then by sticking his hand out at the last moment.
Of course, in some ways this scene just demonstrates one of the problems with magic - it makes escalation too easy; it enables the thought to become the deed. In a real-world, non-magical situation, an excitable teenager who saw an enemy spit in the face of somebody he loved might feel an intense urge to do something dreadful, but all he would be able to do on the spur of the moment (assuming he wasn't carrying a knife or a gun, and that he wasn't the sort of lunatic who kicks people to death) would be to sock them on the jaw, which would be reasonably proportionate to the offence. Even if he thought, at the time, that he would like to punish them by torturing them in extreme ways, this would take a lot of time and effort to set up, during which he would probably cool down and realize he was being ridiculous. But Harry, with his wand, is able to translate that momentary surge of cruelty into instant action.
When she was asked about this scene, Rowling likened Harry to Snape, two flawed men, and it's fair enough that young men are often idiots and may do things they will regret in later life. Nevertheless it demonstrates pretty clearly that Harry is capable of being violent and vicious, and makes an interesting contrast with the scene where Harry calls Snape "Coward" and Snape, in what seems to be an agony of rage and despair, gives way to his violent impulse - and gives Harry the magical equivalent of a slap in the face, which is no worse than what he might have done if he hadn't had magic.
Harry certainly seems Snape-like, i.e. brave and protective but not very kind, when he saves Dudley from the Dementors, but then doesn't bother to tell Vernon and Petunia that feeding Dudley chocolate will make him feel better. Dudley is his enemy, but he saves his life; he saves his life, but he doesn't care about his emotional state.
Although canon Harry is flawed and occasionally nasty, the fanfiction theme known as Dark Harry, where Harry turns out to be truly cruel and evil, doesn't really work unless you're going to assume that he has been taken over and mentally corrupted by Voldemort. Canon Harry is unselfish and devoid of self-interest to an unusual degree, so he would have little motivation for becoming an Evil Overlord. Film Harry may haver between saving Cedric from the Acromantula and winning the Tri-Wizard Cup, but book Harry doesn't hesitate for a moment.
Indeed, given that Harry has managed to be as reasonably-good as he is in the books with a Horcrux sharing his body, he may at base be as virtuous as fanon makes him, in order not to have been corrupted any more than he is; and it may well be that having been de-Horcruxed he would grow into a thoroughly good man (although this isn't really the case in The Cursed Child, if you accept that as canon, which personally I don't).
Dumbledore habitually offers people sherbet lemons.
[Or lemon drops, in the U.S. editions. I gather that in the U.S. sherbet is a fruit sorbet containing cream, but here it's a white fizzy powder which crackles on your tongue, and a sherbet lemon is a hard, boiled, translucent yellow lemon-flavoured sweet shaped like a rugby-ball and with a hollow in the middle containing fizzy sherbet powder. They are similar to a sweet called a Zotz which is sold in the US, except that a Zotz is a sweet hard candy containing a sour powder, and a lemon sherbet is a sour hard candy containing a sweet powder.]
Sherbet lemons, from Amazon advert
In the very first scene in the very first book Dumbledore - who we now know had just come from verbally lacerating Snape while he was in an agony of grief, almost certainly because Snape had accidentally reminded him of his own guilt over his sister Ariana's death - deflects McGonagall's questions about the death of the Potters by childishly concentrating on sucking on sherbet lemons, says that he is fond of them and offers one to her. In CoS "sherbet lemon" is the password to the stairs to Dumbledore's office. The sweet is mentioned again in GoF when Harry twice tries it out as a password although it no longer works. And that's all.
Dudley Dursley is fat.
As a baby Dudley's head looked like "a large pink beach-ball wearing different-coloured bobble hats" and he is described as "large" in all the photographs of him as a small child. He is a very fat ten-year-old and has probably been fat for some time, since we are told that Harry wears Dudley's cast-off clothes which are four times too big for him, and it sounds as if this is meant to be a long-term thing. We're told that ten-year-old Harry is small and skinny for his age, so we can say, very loosely, that if Harry is half the clothes-size of an average ten-year-old, Dudley must be twice the average size. Even if he's tall for his age he must also be pretty fat, and indeed he is described as waddling, as looking like a pig in a wig etc..
Many fanfics, and the films, therefore portray Dudley as fat wherever he appears. In canon, however, he's only fat until the start of GoF, at which point he is put on a strict diet on the orders of the Smeltings school nurse. Following this he takes up boxing and in the later books he is beefy and muscular (possibly also between the ears), not fat.
Aberforth Dumbledore is a better person than his brother.
When the Trio end up at The Hogshead in DH, Aberforth is strongly critical of the way his brother's schemes were always likely to get his followers hurt, and his use of underage agents. "My brother Albus wanted a lot of things, and people had a habit of getting hurt while he was carrying out his grand plans. [cut] Nice job, I hope? Pleasant? Easy? Sort of thing you'd expect an unqualified wizard kid to be able to do without overstretching themselves?" This has naturally led many fen to portray him as much nicer than Albus, and more reluctant to involve childen in a war.
A few hours later, however, Aberforth complains about having had hundreds of students evacuated through his pub, and says "And it never occurred to any of you to keep a few Slytherins hostage? There are kids of Death Eaters you've just sent to safety. Wouldn't it have been a bit smarter to keep 'em here?" and Harry replies that Albus would never have done it. It seems, therefore, that Aberforth is at least as ruthless as his brother, when it comes to using children as tools in a war - so long as they're Slytherins.
The Hogwarts letters sent to Muggle-borns arrive on their 11th birthdays.
There is quite a common assumption in fanon that because Harry gets his Hogwarts letter directly from Hagrid on his eleventh birthday, all Muggle-born students get their Hogwarts letter on their eleventh birthday - even if their birthday is on 31st August. If you count back from Harry's birthday to the day the first copy of his Hogwarts letter landed on the mat, however, he got, or should have got, his letter on 24th July, a week before his birthday. Hermione on the train says that she has "tried a few simple spells just for practice" and has "got a few extra books for background reading", and that she has been "asking around and I hope I’m in Gryffindor, it sounds by far the best", all of which strongly suggests that she found out about the wizarding world only recently - not on her eleventh birthday which was nearly a year ago. So we can be confident that the first years' Hogwarts letters normally go out in mid to late July, regardless of when the student's birthday is - although one would hope that they would be sent out earlier to the sort of family where the parents would otherwise already have booked their children in for a fee-paying school, and started paying in advance.
If, however, you accept Pottermore as canon, a Pottermore essay on Minerva McGonagall's back story says that she received her Hogwarts letter on her 11th birthday. From the dates Rowling has given on her website and on Pottermore, Minerva was borh on 4th October 1935, so her birthday definitely wasn't in the summer holidays. So if you accept this as canon, in the past the letters did go out on people's birthdays.
I've heard somebody argue, as a reason why it was unfair of Snape to ask Harry about the contents of one of his set books, that Harry had only been to Diagon Alley and bought his textbooks two days before the first Potions lesson. This idea comes from the films, in which it appears that Harry goes straight from Diagon Alley to King's Cross. It's true that in GoF Molly Weasley indeed collected the children's set books for them from Diagon Alley only a few days before the start of term, probably due to the disruption caused by the World Cup. But in the books, in PS Hagrid takes Harry to shop for his new course books, uniform etc on his birthday, 31st July, so that he has a whole month between buying his books and starting at Hogwarts, and we're told he spends that month taking a great interest in his new books and "[lying] on his bed reading late into the night". In CoS they get their letters detailing the books they will need for the coming year a week after Harry arrives at the Burrow, which is about ten days after his birthday, and they buy the books the following week - so in mid August. In PoA Harry leaves the Dursleys' place and goes to Diagon Alley a week after his birthday, then spends "several days" settling in, then buys his books for the next year - so again, in mid August.
In OotP their booklists do indeed arrive on the very last morning before the start of term, and Molly has to dash to Diagon Alley to get them while the children are packing - but Ron says "Booklists have arrived. About time, I thought they'd forgotten, they usually come much earlier than this ...' In HBP they do their shopping only a few days after Harry's birthday. So we can safely say that by Harry's time first year Hogwarts letters, at least for those who hadn't known before that they were going to Hogwarts, come in mid to late July but the booklists for later years may come two or three weeks later. Shopping for the next year's course books and equipment is generally done in or around the first half of August.
Lupin has yellow eyes.
The idea that Remus Lupin has wolf-like, yellow or amber eyes is pure fanon. If you go by the original editions of the books alone then it's an idea which is arguably canon-compatible, since his eye-colour is not specified in the books. Yellow-eyed humans do exist - but they are however very rare. That I'm aware of I've seen two in my life, both male, both redheads, both - weirdly - working in the same shop at different times, although they were not related. You could say that the assumption must be that Lupin does not have yellow eyes, since if he did they would be unusual enough to be noted, as they are for Rolanda Hooch.
The later, special illustrated Limited Edition of the books includes a picture of a Ministry file about Lupin, which states that his eyes are in fact green. It's a matter of taste whether you consider an illustration to be canon or not. The illustrations in the initial US editions, giving Snape a goatee beard, are not considered canon but an illustration which contains text is a little different, and could be compared to the lists of borrowers and readers' hand-written notes in the Quidditch Through the Ages and Fantastic Beasts and Where to Find Them booklets, which are considered canon. I don't know whether it's known whether Jo Rowling provided the information shown on Lupin's Ministry ID sheet or not.
The Dark Arts and Dark magic are obviously, intrinsically evil
I actually have a full essay about this called Sectumsempra and the nature of curses, which looks at what we are told about the different classes of spell including the Dark Arts and Dark magic, and concludes that these terms refer to any magic which is alternative or unauthorized or dangerous in some way. This can mean anything from monstrous evil which warps the very fabric of space and time, all the way down to Goth lifestyle accessories.
For example, we are told that everything which is on offer in Knockturn Alley is Dark Arts-related - and then we are shown, more than once, that Hagrid shops in Knockturn Alley. Whatever the Dark Arts are, therefore, Hagrid does some of them. We're told in Beedle the Bard that Beedle - and Dumbledore - merely "mistrusted" Dark magic: not that they recoiled from it in revulsion.
In the Spinner's End scene, Snape tells Bellatrix that when Harry arrived at Hogwarts there were rumours going around that Harry "was a great Dark wizard, which was how he had survived the Dark Lord's attack", and he's telling the truth, because Ernie Macmillan says in CoS that "Only a really powerful Dark Wizard" could have survived the Killing Curse. We know that Harry survived because of Lily's sacrifice, but nevertheless the wizarding world in general clearly considers it possible for a fifteen-month-old baby to already be "a great Dark wizard", able to use his powers to defend himself. Whatever a Dark wizard is, therefore, it clearly isn't, or isn't necessarily, a person who consciously performs acts of evil magic.
The power of the Obscurus, the manifestation of a child's pain and bottled magic, is also described as dark. At least some of the things classed as Dark seem to be things you do with your will rather than a spell. Snape comes across as more like a genuine magic-user than most of the characters, especially in the way he sings Draco well - so perhaps the reason he wants to be a Dark wizard (if he really does) is because he's a real magic-worker, not just a spell-caster, and he wants to work with the real raw stuff and shape it with his mind. Which would either be wonderfully liberating or a good way of getting fried, depending on exactly how good his control is.
Hogwarts students wear regular Muggle-type school uniforms with academic gowns over the top.
The grey uniforms with trousers or gymslips and school ties belong to the films. In the books the students wear black robes, plus pointed hats (even in the classroom, according to Rowling's own drawings). When they put these robes on on the train, we're told they simply take their jackets off and then put the robes on over whatever they are wearing, which in Harry's case means Muggle attire. We don't know whether they continue to wear other clothes under their robes while at school - it probably depends on how cold it is. Sixteen-year-old Snape, on a bright June day, seemed to be wearing nothing under his robes except underpants. Rowling's own drawings suggest that she thinks of the robes as floor-length, dress-like and pulled on over the head, so not showing much if anything of whatever the student may be wearing underneath.
There is a mystery in the books in that students seem able to tell at a glance what house someone is in, but we're never told how (except in the case of prefects, who wear pin-on badges), and their first-year robes are bought before they know what house they're going to be in. Perhaps house-elves sew appropriately-coloured piping or embroidered patches onto their robes once they've been Sorted, but if so we aren't told about it, and there's no mention of the uniforms and ties seen in the films which, if they existed, would be on Harry's summer shopping list for Diagon Alley.
There is, however, a strange anomaly in OotP, where Draco says "Weasley, your shirt’s untucked", and takes points because of it. This is a school day - they've just come from Herbology - but Ron is clearly visibly wearing a shirt, and something to tuck it into. It was just before Easter (it was the day after the betrayal of the DA, which happened on the day of their last session before Easter)so the weather may have been cold, but that doesn't explain why Draco could see Ron's shirt.
Perhaps school robes can be of any design so long as they are plain and black. Percy in Rowling's drawings is wearing a pull-on one, but Ron's robe in fifth year opens at the front, so that if he chooses to wear anything underneath, it will be visible. Or maybe he just took his robe off for Herbology. Either way, whatever is worn under the robe isn't uniform, since it isn't specified on the shopping list.
I'm wondering if they intentionally sell different uniform styles, or if maybe the time when Harry was a student was when the uniforms updated?
I think the uniform robe are flexible, it is upto the student to wear anything under it. Snape preferred not wearing trousers mostly because they could get in way in case of potions accident. So it is canon compliant that Ron wore open robes in OOTP and Snape had not worn trousers as seen in SWM and PS.
