1948/49 Leaf John L. Sullivan - white pants?
 

A number of cards in this set can be found where an article of clothing is either light blue or left blank white (there's no white ink on these cards; it's just the stock used to serve as white. Jeffries, Greb, Ambers can be found with this recurring genuine variation as a normal matter. I have never noticed a Sullivan with white trunks before.

Now that I have it in hand, I notice that it's not quite devoid of blue. There is a stripe of blue on the crotch, a blotch above the belt, and a few specks of blue ink just to the right of his pants in the red backdrop. Typically, a card like this is easily explained because it is just missing a print color pass; blue wasn't run on the sheet or the machine was out of blue ink and nobody noticed (or, since it is Leaf, nobody cared because QC didn't exist). Doesn't seem like that's quite the case here.

Has anyone ever seen another Sullivan like this?

Looks like maybe the ink ran out.