Yes, in slang "μελανούρι" means "attractive brunette". It is not vulgar.
Μελανούρι literally means Saddled seabream (a kind of fish).
Μελανούρι is a kind of fish. Μελανούρι ψάρι translates word by word to "melanouri fish" but the correct order would be "ψάρι μελανούρι" when used in a sentence (the word ψάρι would most likely be omitted all along). "Mελανούρι" by its own is also slang for "attractive brunette".