We know that the inheritance of eye color is much more complicated than once
believed. It is not under the influence of just one gene, or else people
would be either brown eyed or blue eyed. This also does not account for the
difference in shades of eye colors. Now it is believed that eye color is a
polygenic (many genes) trait and it depends on how many active (additive)
alleles(versions) you inherit. By the way, blue eyes is really an absence
of
color, similar to the way water appears blue by reflection but is really
colorless. So people with blue eyes have not inherited any or very few
active
alleles. The more active alleles that are inherited the darker the color of
the eyes. Let us say that mom has medium brown eyes and dad also has medium
brown eyes, but each of them have 3 active alleles and 3 non active alleles.
Let's say then that their first child inherits all 6 of their active alleles
and has dark brown eyes. Let us say that child number 2 inherits all 6
non-active alleles. That child will have very light blue eyes. Green,
hazel, gray, light brown, etc. are all as a result of how many alleles are
adding to the eye color. This is also why brown is always dominant over
blue
and green is dominant over blue because they both have more active alleles
than blue and add to the eye color.