I like this expression, 烏の濡れ羽色。I checked the internet, and this form, with all kanji, is most common, I think.からすの濡羽色（ からすのぬればいろ ） beautiful black hair. ( black and wet
feather of the crow ). I don't know other metaphors to describe the beauty of the parts of human body.
I have seen women with such hair. The translation into English is very awkward, but I think the image that I get is very beautiful!