There's also the theory that he's brainwashed, too, due to his eyes being blue in The
Avengers and green in Thor. But I don't know, maybe Hiddleston just got sick of the contacts.

I love this very simple and most likely true explanation. It reminds me of how Nick Hornby rolls his eyes at Bob Dylan fans who dissect every single lyric of his and jump on how since this word doesn't rhyme with this word it must have some super-deep meaning. Hornby's explanation is basically, "I think at some point Bob Dylan was just like, 'Fuck it. Close enough.'"