I don't see why not. There are plenty of RPers out there with "unnatural" (pink, green, blue as opposed to "natural" black, brown, blonde) colored hair and now with the aesthetician it makes a little more sense for having it. So I don't see why there would be a problem with highlights.
I suppose it could still make sense without the aesthetician if the character was an alchemist or knew one but that's offtopic.
I suppose it could still make sense without the aesthetician if the character was an alchemist or knew one but that's offtopic.