Purple anthocyanins are antioxidants (red, purple and blue colors). The red corn is Ruby Queen, but the red doesn't usually deepen until the corn is past eating stage so I wouldn't . "Indian corn" is very healthy because of the colors.
There are a few blue potatoes commonly available, mostly related to ALL Blue. If you want cutting edge high anthocyanin or betacarotene potatoes (blood red, blue black, or orange flesh) this is the place (also has blue tomatoes)...