PLEEEEASE tell me he will go back to being blonde

Not in the main story, aside from the epilogue where he should be blonde again.
He dyed his hair and uses contacts for the role of the movie he his shooting for the rest of the main story.
In the side stories he'll be blonde again.

nooooooooooo
At least I'll comfort myself with the fact he will end up blonde at the end

IIrc Josh preferes him as a blond, so I don't think the author will let Chase dye it unless it is necessary for filming.