I prefer coloured toys; black toys always seem too fetishy to me, and skin tones tend to be rather insipid.
If they were the only options, then I'd pick black for a butt plug, and skin tone for a dildo.
I've never seen a toy that was pure white, but I imagine it would show up dirt too easily, which would creep me out.
I made a post on my blog
about my feelings on toy colours.