I prefer bright traffic cone orange, neon green or yellow, or black or dark grey with large components of any of the above colors as contrast, but then again, my primary concern is visibility in busy traffic, not aesthetics.

I also intentionally keep my bikes dirty as I want them to blend in with other bikes on the rack and not look too shiny new to attract the thieves.

Then again, all my bikes are intended for and used for commuting, even my one road bike, which has addon commuting gear now as opposed to when I rode for recreation rather than transportation/utility.