Favorites?
Black and white
Gold and black
All metallic colors combined (but only if it has no other colors)
aaand a very oddly specific color set…
Gunmetal, black, and Skull Spider green, with purple and trans-clear highlights
Least favorites…
Well, not many. Mostly color combos that aren’t pulled off well. Most anything can go well, but it really depends on how skilled the MOCer is.
Ah, you forget, Mata Green was not abandoned following 2003. 2006’s Mini Tractor, 2009’s Tractor with Trailer, and 2013’s Service Truck all had mata green parts in them. Several technic vehicles prior to bionicle had the old green too which actually makes it a pretty serviceable color if you know what you’re doing.
I like a good dark red and a light teal. Purple’s awesome too.
Least favorite? Uh… Not too big on orange, or any neon color. Those just hurt my eyes to look at.
Anything with purple pretty much becomes my favorite.
My favorite color scheme has got to be Onepu purple and lime. I also like silver and Metru blue, Metru green and Keeto orange, and maybe Metru red and white. I love the three main Metru colors, and Onepu purple might just be my favorite LEGO color ever. Transparent green is probably second.
I can’t stand the neon transparent orange, not because it looks bad, but because it’s often overused. I also dislike the sky blue of Nokama and Gali 2001.