No - just for women. I can't think of a word which means "a man with dark brown hair". Perhaps others can?

As a hair colour? Yeah I'd use that term for a man's hair and a woman's hair

No, you can't. 'Brunette' is only ever used for women. It is never applied to men, boys or even to little girls. It's a French feminine diminutive. It's also a teeny little bit old-fashioned, patronising and sexist. If you want to be political correct, you might do well to avoid it. A dark-haired woman or a woman with dark hair is fine - there's no need to use a cute little diminutive.

"Brunette" is for women with dark brown hair. If you talk about a man, you should say "a man with dark brown hair" or "brown-haired man".

"brunette" is a french word that means "dark brown haired girl" the male equivalent of "brunette" could be "brun ténébreux" which is an attractive dark brown haired male