Zena has white (semi-transparent) toe nails except for one which is black. I like this color because I can see how much I can clip. I don't know about genetics of toe nails though.
How funny, Finn is the same way with all white nails and one black. Actually it is half black. They were all white until he was about 9 months old. I thought perhaps the merle contributed to that but I don't know. I agree that having the transparent nails makes clipping much easier.