I didn't say a word about anyone caring, so I'm not sure why you're saying this.
The point I was getting to was that many wouldn't care, partially because many don't know and even those that do wouldn't find it a significant enough detail. The whole "debate" began on the premise that no one would care if there was a "twist" ending resulting in Joker being permawhite.
Patently false. People remember whatever they remember, whether it's worth it or not.
Memory is not random. Memory is made through meaningful association (pleasant or unpleasant) or rehearsal: liking something about the movie enough to convert the short-term memory into a long-term one or watching it multiple times. You don't just remember whatever you happen to remember; there is a process.
I didn't say they had to remember everything about the film--they just have to live in North America. Whether it comes from the film or from somewhere else, the "general audience" knows the Joker's skin is white, by the same token that everybody knew in 1999 that Darth Vader was Luke Skywalker's father. They didn't walk into The Phantom Menace thinking "Oh, who is this guy?"
We can debate forever about which specific details of movies people remember but the point isn't that the general audience doesn't know that he is permawhite, but that so few would remember the specifics and/or find it an integral part of the character that they wouldn't care if Joker was merely painted white. There is a good portion of people who just know the Joker is
white regardless of how he became that way.
And, of course, there's no reason for them not to remember. This "Oh, they don't remember some blockbuster!" line is silly. They remember details about a million other blockbusters, why not Batman? Batman is more culturally saturated than, say, Indiana Jones, and nobody has trouble remembering comparable details in those films. I haven't seen The Last Crusade in fifteen years, but I still remember that Indiana was the dog's name. And, unlike Joker's skin, that was an obscure detail, unimportant to the film. The only people who might not remember are those who were very young at the time (and even that's a long shot), and even if they forgot, they eventually would have figured it out simply by virtue of living in North America, where you can find the movie playing on cable every month, along with a constant line of cartoons, comics, games, toys, and millions of people who will tell you the fact of the matter. If you know who the Joker is, you know his skin is white, in the same way that anyone who knows of Batman knows his parents were killed, and anyone who knows Darth Vader knows he's Luke's father. People who have never seen the film will know it, by the same token that I know how from Planet of the Apes ends without having ever seen it.
But you don't necessarily know
how it became white. The only completely mainstream version of Joker's origin that the general audience would see is Batman '89 and there are plenty of reasons for them not to remember that he fell in some acid.
But I don't really care whether they know it or not because the average person's knowledge of it would be so cursory that they still wouldn't give a crap if Ledger's Joker became permawhite in some weird twist. Neither of us can completely assume what people know/don't know about the Joker but I completely agree that people know he is white; I don't agree that the majority remembers how or why he is white and as long as Ledger has a white face, they won't care.
And someone else's line about Joker having no makeup on when he is a cop is inconsequential: he put on makeup in Batman '89 for the same effect.
Again, this is patently false. Batman is not just "another blockbuster." Batman is a cultural icon that's become a part of the cultural fabric of the entire continent--and whether a person likes, hates, or doesn't give a damn about Batman, everyone recognizes the the saturation of the icon, and there are things that pretty much everyone knows. They don't have to care in order to be familiar with it, just as a million people who don't care about Star Trek can still give you general information on Mr. Spock.
There will always be people who fall through the cracks, and by some miracle don't know the things that everyone else does. But they in no way make up a majority of the general audience, and I would bet they don't make up even a significant portion of it.
Again all of this boils down to people knowing that Joker is
white, not permawhite. I've acknowledged that much before you ever responded. It is a pointless debate to try and assess exactly how much of every cultural property everyone knows and doesn't know. The ultimate point is that for most the detail about Joker wearing makeup to be white and being permamently white is completely inconsequential; it would be different if he suddenly became green and Hulked out, but he still very much fits into the general audience's expectations of what they know about the Joker. Changing him from normal to permawhite during the course of the movie won't have a significant effect.
I watched an interview today in which Kevin Conroy called Bruce Wayne's father Bruce Wayne Sr. I'd expect the longest running actor to play Batman to know that, but he forgot. Sure, we can argue that that detail is inconsequential and the Joker origin isn't, but Conroy IS Batman, and to the average person the details of Joker's origin ARE inconsequential; it isn't like falling into a vat of chemicals is a new prospect in comic books.
This argument won't go anywhere and it will do so pretty quickly. I am not disagreeing that Batman is a cultural icon--that much is obvious--but the differences between Ledger's Joker and what could be called the common perception of Joker are so minute that most audiences wouldn't care (which is the whole point of it whether you stated it or not); especially about some thrown in "twist" making him permawhite.