We people living in India have seen black crows, even grey or dark metallic blue crows and we often use a sarcastic statement in which we refer to an imaginary white crow. In fact, I myself have indulged in such sarcasm. Henceforth, I promise not to use that statement as I have indeed seen a lot of white on a crow and it is indeed present in the world.
I got an idea about this when I saw the Pied Crow at Lake Nakuru National Park in Kenya. This crow has a healthy amount of white on it and stunned my fundamentals, which always thought white on a crow could only be seen in dreams. But, not anymore!!