Welch's purple grape juice is concord grapes: "In the United States, 417,800 tons were produced in 2011.[3] The major growing areas are the Finger Lakes District of New York, Lake Erie, Lake Ontario, Southwestern Michigan, and the Yakima Valley in Washington.[4]"

You can use it to make wine just fine, if you're in to that sort of thing.

If i had to guess the white grape juice is whatever the green seedless variety in california was for decades from the late 70s on.