I use Photoshop because it is loaded on most of the computers at my school. I use adjustment layers to tweak the hue and then erase everything I don't want colored. Or their are other ways to do it. Also if you don't want to pay big bucks for photoshop then their is a free program called gimp that is similar. I have never used it personally but I know some people who do.
Why are you wanting to get started? I could do you one or two if you just want a couple color changes.