I found this reference:
Heirloom Potatoes: 2000s Archive : gourmet.com
Potatoes come in all the same natural colors of the other members of the genus Solanumto which they are botanically related (eggplants, peppers, and tomatoes, for example). Generally, this means red, purple and blue (the color varies greatly due to soil), yellow, orange, pink, and white.
The natives of the high Andes, where potatoes originated, enjoy thousands of different varieties and colors. They shrug off the potatoes we grow in North America and Europe as rather bland and uninteresting, yet to us many of their potatoes taste somewhat bitter or sharp. This is because potatoes with a lot of pigments in the skin or flesh carry different genetic material inherited from wild potatoes, which rely on their bad taste to fend off animals. This natural defense system is still present in the plant itself and is toxic to humans and many animals. It is also found in potatoes that turn green (a sign that theyve been improperly exposed to light), so never buy potatoes with green spots on their skin.
Interested in growing your own heirlooms?
Contact Seed Savers Exchange in Decorah, Iowa (319-382-5990).