I don't know a lot about yorkie coloring genes, but I do know about horses
With horses, you can get a "double dilute" (perlino or cremello) or just dilute, which is dun. Dun can show up in any coloring of horse, a bay dun will look almost the same as a buckskin, a black dun is a grullo (I have one of each!), there are all sorts of dilutes in horses. I would think, but I am not sure, that similar things can happen in yorkie genes as well. Can you get a double dilute yorkie?