SillyThought: Do we hate blonde male superheroes?

Paranoid?

Thor has had short hair in the comics.

He's animated, but also, the one in Into the Spider-verse and what happened to him.

CH and CE were never blonde to begin with.

Just like SJ was not a redhead.

Once the characters were established, they let them gradually return to their real hair colors.

JM is a separate case, ZS cast him to ( try to ) make Aquaman into a badass.

Wonder Woman got to keep her blond-Steve Trevor (granted, his was a dirty blond in the movie, but that's cause Chris Pine isn't a natural blond, so they probably got as close as they dared without making him look like he was wearing the world's worst bleach job), and Black Widow became a blonde for some reason in INFINITY WAR.

I think, sometimes with the new movies, it is because of them not-hiring blond actors. Think back to FANTASTIC FOUR with Chris Evans & Jessica Alba, neither are natural blonds and both were made to have blond hair for the movies. They played a little with Chris Evans's because they could cut his so short that you didn't notice so much that it was a dark-blond, but Alba was made fun of by fans/moviegoers for the horribly fake looking blonde hair and blue contacts utilized to make her look more like the comic book character, and they darkened her hair a few shades in the sequel, as well as Evans's, and it looks more natural on him, less distracting on her.

For THOR, Hemsworth had blindingly white-blond hair in the movie and it looked horribly fake. Hiddleston's ink-black and chemically straightened hair looked fine, Hemsworths brown, straight hair turned blond looked like he had taken frosted tips a bit too far or like a dark haired guy who got lost at sea for a couple weeks, then got to be in the shade for a few weeks. In the second THOR, they tamed down the bleach job and it looks much better. In THOR3/INFINITY WAR, I think they also wanted to further distance him from his Princely/heroic look-- he has darker colors, his metal pieces aren't as shiny/polished, his eyes aren't lit to make them as pale-blue looking so he has darker (stormier, shall we say?) blue eyes, his hair darkens, and he doesn't smile anymore.... I suspect it was much the same for Steve, in AVENGERS he just woke up less than a month ago so he's basically FIRST AVENGER Steve with culture shock and grief-stricken. By WINTER SOLDIER, he is sporting a more modern haircut but the color is a bit more honey-blond than gold-blond, and by ULTRON it actually had some hints of brown at the back of his head with only the top layer retaining the amber/honey color, but he's also wearing a darker uniform (WINTER SOLDIER he sports his stealth suit that is all navy/dark blue with hints of scarlet - in ULTRON it is a darker blue with an off-white and dark-red stripes/etc., compared to his blinding AVENGERS 1 suit that was brighter than his FIRST AVENGER suit as it was made by a man who was going off his idealized versions of the war bond posters and playing cards), and in INFINITY WAR he has a grungy uniform and has been undercover/on the run for a long time so he may even have dyed his hair just as he grew out the beard to make himself less recognizable, plus it is a breakdown of his military/Avengers identity/regiment where he was always clean shaven and perfectly coiffed, and he also gets the less-well-lit eyes, less smiling, etc. that Thor got.

Kind of like if you watch MULAN, how she looses her eyelashes and her eyebrows get thicker when she goes from Fa Mulan to Ping at the training bootcamp, then when she goes to being Fa Mulan With A Sword she has her eyelashes back but her eyebrows remain thicker. Subtle differences in the animation to help distinguish her changes as a character. Make up, hair, lighting, and wardrobe are used in the live-action to accomplish the same thing.