I like the oranges and browns because they are warmer tones that offset the figures...but I also like the green because it feels nice as a background, even if it is close to the first two characters' skintones; it's also very different to the third.
I could also point you to Wally West's "22 Panels That Always Work" for some other ideas regarding background and composition, if perhaps you might like to incorporate them in future. They've always helped me when I'm stuck.