The typical coloring of Californians depends on the Himalayan gene, which is temperature sensitive. If it’s very warm, the coloring can revert back to white or light gray. If it gets very cold, f ex if a kit falls out of the nest, the kit can develop a “sooty” fur anywhere on its body.
My guess is your bun has one parent that has 2 copies of the gene and one parent that doesnt have the gene. Or two parents with one copy of the Himalayan gene each. White tips of ears (the very rim of the ears, white underneath the tail and/or white around the nostrils) means the rabbit can’t be shown as a Himalayan, which is of absolutely no importance unless you’re planning to show or breed your bun.
The dark fur on Himalayan rabbits get a darker in winter and lighter in summer. (I’m saying Himalayan rabbits because California White is a breed, but Himalayan is a color-gene that can be carried by lots of different breeds, f ex Nethies and mini lops.)
It is a super cool gene. Your bun is also adorable.