Is there a safe way to change the color of an iPhone?

I'm tired of my old black iPhone. Is there a way to paint it without damaging it or what?

I don't think there's a way to paint it without damage, even children stickers can damage over time and you don't want to risk what happens to when your iPhone over heats, since most paints are flammable, my best suggest is to get a phone case. It's easy, cheap and looks nice and even protects your phone and you could change it when ever you want, hope I helped.

Color it with crayons

Basically, no, there isn't a safe way to do it. Do you want a reliable phone, or a fashion accessory? You will probably change the current phone for a more up-to-date model eventually, so if it really bugs you, change it sooner rather than later. Get one of the models which have interchangeable cases of various colours.