I would love colors, and I do imagine they will come eventually but probably not until they need something to throw into the mix for difference. This iPhone has enough upgrades and changes without new colors to be new enough. Maybe next time when a 5S comes along they'll release new colors to give reason for change.
I'm actually surprised that they went with colors for the iPod Touch, I'm glad they did but it's a bit surprising that all of a sudden they're considering colors as a nice fun thing. Reasoning behind colors I'm sure is because people who buy iPod Touch's and iPod Nanos are usually young, or they're bought for younger people. Kids. That, and iPods are pretty personal but at the same time a lot of people have them so giving yours a little personality over other people's is pretty nice. With phones it's not really like you leave them around or would ever lend them to a friend or anything like that. I don't know if I'm explaining this right.