Buy whatever colour you want and then get a
Gela Skin to cover it! You can even create a custom skin (if you don't like any of their artists) if you would like. I've been trying to force a more arty friend of mine into making me a decent 'Hitchhiker's Guide' looking cover, but she's being slow so I can't tell you if they're a decent quality or not from personal experience. But at least it wouldn't matter what colour Kobo you get.