I like the idea of having a glitch piebald mutation, they can be in both black and white, with one color slightly showing.

I.E if you have a black colored piebald mutation hints of the white piebald mutation will show and vice versa.

However I'd make it pretty challenging with a 13% chance of 2 parent piebalds passing them both down to one cub.

I'm not good with coding but I really like this idea