My mother has very dark blue eyes (her siblings have grey, brown, blue, and hazel) and my father…

Yes, I would appreciate if the author would go into more depth about the different shades of these colors, but it is logical to assume that the differences are just dependent on the ratios of the things he did explain.

So for dark blue eyes maybe there is a thin layer of melanin so the light blue that it would be if there was no pigment is just shaded a bit by the layer of what would be brown (melanin) and the result is a darker blue (?)