They're not blue. They're a greyish brownish color... (Tab and I have argued over whether it's grey or brown). The "blue" is actually the white of the eye.
I suspect it's a similar modifier to the type in humans. They appear silver in person and it's not likely I'm going to get her to hold still under a scope to let me get a good look. )
I had a pure white with navyblue eyes. I think it's ressesive, because it only appeared in some lines her in Norway. I think there has been 5-6 of them. 2 of them were close relatives, one brother and one nice.