The extremes of red-tailed hawk color morphs. White to very, very dark. Both are the same species, Buteo jamaicensis.
The bird on the left has an extreme lack of melanin production and the bird on the right over-produces melanin. Melanin is produced by cells called melanocytes, which also produce pheomelanin, which results in a reddish-brown color. Note that the bird on the left has a red tint to her tail even though her melanocytes aren’t functioning normally, this could be due to porphyrins and/or carotenoids contributing to the red color in red-tailed hawk tails as well.
Both birds still exhibit the common trait of being total derps (as demonstrated in the third set of photos).