Gold, brown, & cream
Light blue, leaf green & royal
Hot pink, turquoise, purple, white & silver
White, light pink, baby blue & silver
Purple, turquoise, blue & silver
Yellow, turquoise & royal
Or, you could use varigated ribbons - that fade through the rainbow, or one from one color to white? You could really go nuts with different fancy ribbons. (I like the plaid ideas, too)
Just thinking about some of the combos I have for my horses.