My neighbor, friend, irrigator, helper asked me if I would paint a white buffalo on his buffalo skull about 2 years ago. Well I finally got it done. Painting on skulls is definitely a different surface.
After talking to other artists who paint on skulls, I prepared the skull by first making sure the skull was clean and then sprayed it with a clear acrylic spray paint. After that dried, I used acrylic gesso on the forehead where the major painting was going to be.
I decided to keep it pretty simple, and just paint a bull portrait. I drew the portrait on and then kept the background in sky blue and then winged it for the color of the buffalo as I have never seen a white buffalo. I have seen many pictures, only to find out that they crossed buffalo with white domestic cows so they were not true color of a white purebred buffalo.
I also found out that most buffalo born white turn back to the browns of normal buffalo with age. So I kept the head dark for contrast and used lighter color for the hump and back.