F.M.
I like tan/beige/browns, adding pink to the girl's side of the room/crib and adding greens (earthy olive greens) to the boy's side of the room/crib.
If you are more "Bold" then you could always do primary colors all over - red, yellow, blue, and green. Girly polka-dots on her side, Boyish stripes or solids on his side.