I don't think I've ever seen a white PC.

Could you get something like you have above and have white fabric sewn over it? You could see if any tailors in town would do it for you. The fabric would need to be thick enough to conceal the original color.

Be aware, some reviews of the PIG Brig (your first pic) say it sticks up too high in the front to conceal. So you'd need to start with something lower profile or with adjustable front straps.