"White barbecue sauce" sounds like an oxymoron, doesn't it? I passed it on supermarket shelves for years not knowing what it was, because I thought barbecue sauce had to be red-to-brown. But so well established, it has an entry in the Encyclopedia of Alabama. You'll find a variety of recipes for "white" or mayo-based barbecue sauce online.

I couldn't get the E of A link to work, but here's the text (though it's boosterish in saying it's "unique to Alabama" now that it's spread to other Southern states): "White sauce is a type of barbecue seasoning unique to Alabama. It was created by Robert Gibson, owner of Big Bob Gibson's Bar-B-Q in Decatur, in 1925. The sauce is a combination of mayonnaise, apple cider vinegar, lemon juice, black pepper, and salt and was initially used only on chicken."