They can be any color you want them to be. I've seen brides wear blue shoes, so that they can take care of the "something blue" with their shoes. I've also seen brides wear RED sandals with stiletto heels, and neon pink tennis shoes. It's really up to you what color shoes you wear, especially if your gown is floor length, and no one's really going to see your shoes much anyway. If your shoes will be seen though, you're probably going to want them to match, somewhat.

The one thing your shoes better be is comfortable. Remember, you're going to be on your feet ALOT on your wedding day, and the last thing you want is sore feet halfway through the reception. And if you've bought a pair of high heels, and you take them off, then you're stepping on your hem, because it was hemmed based on you wearing high heels, not going barefoot. Good luck!