I can certainly sympathize with you. I love to take pics of animals but I found out that it is generally more difficult to take good photographs of black ones. I have 3 cats and 2 of them are black and a lot of the times I'm disappointed with the photographs I take. Outside pics can also be problematic, direct sunlight has the habit of turning them into black blobs.

I agree that is quite frustrating, I have lovely photos of the other ones, of strays etc. What I tend to do is to take more than I planned, one of them is bound to turn out decent.

I'm sorry that I can't be of more help I just wanted to let you know that you are not the only one with this problem...
Perhaps someone with more technical knowledge can give more advice?