If you want to really go crazy and start doing fun photoshopping projects on every ring you see, you might want to look into a little application/program called GIMP.
Basically it's Photoshop, but free. For recoloring these kinds of things, all you have to do is either select (magic wand) and separate the stone to a new layer and colorize it, or adjust opacity and color over the existing with the paintbrush.
Should take about 5 minutes or less per picture! =D