Puppy at 6 weeks [A, B] and 7 weeks of age [C] with littermates [D]. As an adult Dog [E].
The KIT gene is responsible for a multitude of white spotting patterns across many species. One of the latest to be discovered is a de novo mutation (a genetic mutation that neither parent possessed nor transmitted) in the Weimaraner Dog. Weimaraner's are generally solid colored and homozygous for both Brown and Dilution. (More about Brown and Dilution) You can therefore imagine the breeders surprise, when their supposedly purebred litter, contained a female puppy with what appeared to be an Irish Spotting White pattern, (More about White Patterns) including, a blaze face, white collar, belly and feet. When genetic testing verified the parentage of the litter, the mystery deepened until further testing reveled the culprit: a 3-bp deletion in exon 13 of the KIT gene. As an adult the female retains all the areas of white but also seems have a general lightning of the coat. It is speculation at this point whether this is an actually lightening of the individual hairs or the result of white hairs interspersed in the coat. With Weimaraner's already possessing light coats such white hair may be easy to overlook and KIT genes are well known for adding "roaning" to the coat (ie Dominant White, and classic roan in horses).
Gerding, W. M., Akkad, D. A. and Epplen, J. T. (2013), Spotted Weimaraner dog due to de novo KIT mutation. Animal Genetics. doi: 10.1111/age.12056