A nuance regarding hair

There’s a particular kind of complimenting hair that’s usually more or less socially acceptable:

If someone you interact with regularly gets a haircut, it’s usually ok (and often expected) to compliment the new haircut. (So long as it’s not done in a way that sounds like you’re insulting the old one.)

It’s very different from out of the blue telling someone that their hair is nice, or telling someone you just met that they have attractive/adorable/pretty/exotic hair.