Though I haven't yet done any kind of comprehensive colour/marking reference, I decided to play around and see what a kellashee with a leucistic mutation might look like.

From Wikipedia: Leucism /ˈljuːsɪzəm/ is a condition in which there is partial loss of pigmentation in an animal resulting in white, pale, or patchy coloration of the skin, hair, feathers, scales or cuticle, but not the eyes. Unlike albinism, it is caused by a reduction in multiple types of pigment, not just melanin.