I've painted an object with one color in texture paint mode. I'm trying to make 4 different versions all in different colors without re-painting the whole object again. How can I switch texture paint colors?
You have two colours available under the colour wheel, press X to toggle between the two while painting.
While it hasn't been added to the manual, you can create palettes of colours to easily switch between common colours. You can find some info about using palettes at the bottom of these release notes.
After you have finished painting one of your colour versions, go to the UV/Image editor and save a copy of the texture image with a unique name so you have each version available later.