I have read that Black Cats are not as likely to be adopted for some reason, I was at PetsMart one day and our SPCA had several Black Cats in various shapes andsizes and they were 25 dollars to adopt.
I woud have taken one, but they know that I have a lot of Cats , and will not adopt one to me.:
I do not think that Black Cats cause more allergies than lighter Cats , but you could ask your Vet.