So I nattered on my Tumblr about mermaids in art and what I don't see but want (and can't make myself due to lack of talent). If I were an artist, I’d draw Irish merpeople. I...
Shared here in case some SL artists might find it inspirational.
An interesting view. True that a new interpretation would be refreshing. I hope some artist(s) will take up the challenge!
One thing, though: a dark skin helps against UV rays. So unless the merpeople live close to the surface they do not need to be dark in warm waters. If anything, they'd probably me mostly translucent.
But that's be being all science-y over something that is arts-y! 
Tanarian
says
If they're cetacean-type, then they'd spend a lot of time up top.
Tanarian
says
And I know porpoises can sunburn; sunblock is common first aid when they're treating beached ones.
Tanarian: Hm. Good point! 
[lives] near the Seaquarium and where they filmed Flipper.
StereoNacht: Translucent would be different. nods approvingly at the thought
T. A. Lowery
shares
These are of my siren, Belladonna, (who EATS mermaids) warning: NSFW 
oooh, I like the viciousness... another trait not often seen in one of those who isn't otherwise drawn as a skeleton with scales
Orca mers. Lantern-fish mers, Humback mers?
There's selkie and such, but they don't look any different other than their hems.
Different from humans - not enough words again.