you just soaked it in 40% hydrogen peroxide 60% water, or you boiled it in that mixture?
I simmer in water first with dawn dishsoap. The soap helps cut the grease. Don't overboil ! I run this bull for maybe 2 hours in the first boil. Then cleaned as much meat off the skull.
Then I simmered in a fresh batch of water and dawn for 1 hour. This second boil cleaned it up real good. After the skull dries, I use a 40% peroxide mixture that I purchased from a beauty supply store. It's used as a hair dye. Take this stuff and brush it over the entire skull and cover with saran wrap or a plastic bag for several days. Rinse well with water and you should be done. I did a second batch of peroxide to make him nice and white.
One thing to consider is doing a degreasing soak in dawn and water , some people even use coleman fuel to fully degrease the skull.
Make sure to keep the antlers out of the water and no peroxide on them as well.