This is leucistic or also known as Panda variation. It is rare color mutation that produces white and black color. Some we even get all white. 

Other color morphs include all blue, all black melanistic, or all yellow xanthic.

The American bullfrog (Lithobates catesbeiana) is the largest frog in North America. It is native to the eastern United States and can be found in every state east of the Mississippi River. American bullfrogs are nocturnal and can be found in or near large bodies of water with emergent vegetation. They are light green, olive, dark green, or brown above, with a creamy white underside and a yellow throat.