I think that bold colors on someone with braces would look great! I've never had braces, but the only concern that I can think of is the color transferring to the braces, like getting lipstick on your teeth. To make sure this doesn't happen, I'd recommend using lipsticks that stay put. Long-lasting matte liquid lipsticks seem like they'd be a good choice.
As long as the color stays put, I'd say that anyone can where any color they want!