I don't personally think the Blue Eye gene is separate for one reason. Blue eyes can easily be explained by Leucism. The dark coloring of the eye is pigment, just like in humans. So Leucism is just working with the eyes as well as the skin pigments.

From my eye doctor. I have blue eyes and when he was dilating them he said it should be really quick and I asked why. He explained that blue eyes lack pigment that dark eyes have, so the dilating solution doesn't have to go through as much pigment.

Hope that helps.