Hopeless: Let user select the colors
Some color combinations are easy on the eyes. Others are downright painful, or at least more difficult to quickly distinguish neighboring blocks.
I'd imagine tastes in this regard are somewhat idiosyncratic, so I'm not suggesting you that you hardcode to a set of colors. Instead, some kind of simple UI for selecting the colors. Ideally, this could be saved as a user pref, but if that's not feasible then it would be no big deal to pick my fave colors each time.