With something like a bike, I'll always go for function over colour. But given a choice of colours, I'll lean towards the more pleasing ones: BLACK, darker reds[1], purple[1]. Definitely not anything on the orange-yellow-light green spectrum. White is just silly.
When I bought my Brompton, I established that the lovely purple that the Birmingham Bromptondock ones come in wasn't an option and went for default black.
[1] I suspect it's no coincidence that I have a preference for colours that - with my vision - occur rarely in the real world. In a world of blues, greens and generic poo colour, it's the deeper reds that are interesting, even if they become black in low light.