Here's a little purple one I found recently. It's from Peru. The orange one was sold as a Garnet Yam, but it's technically a sweet potato. I wish I could find some of these colorful varieties grown locally.
The sweet potato was roasted yesterday then refrigerated. It makes a great snack. The purple one is uncooked, although I'll have to cook it now that I cut it for you to see inside. Funny how different in color they look from different angles.
B just sent this photo stream from the BBC. He knows I'm on a potato kick: