Paper in review on ancient e allele found across a number of current breeds and landraces, and found present in the DNA samples of over 10,000 year old prehistoric Siberian and South-Eastern European dogs:
Coat color genetics is a very intriguing topic. I have rudimentary understanding of it but I always defer to the experts. That article is very informative and prompted me to continue my research on the subject - my poor brain.
It's something I'm involved with for a living, and we learn something nearly every week! If it helps you feel better, human geneticists I've talked to say that we know more (and therefore there's more complexity) about it in dogs than in humans :-)