Eli5 : Why do some genes (like skin color) mix and shade upon inheritance while some don’t (like eye color) ?
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Eye color is determined by the level of the same pigment in your iris, that also affects the color of your skin: melanin.
The key difference is the mechanism of how that color is manifested. With your skin, melanin absorbs most colors of light, and reflects back what’s left. Usually a shade of tan/brown, which can range from very light to very dark.
Your eyes are a bit different. Some of the light is absorbed by the melanin, but unlike your skin, the light that hits your iris also travels through your cornea and lens, which refracts (bends) the light, an also scatters it a bit, dissipating some other colors of light. Your resulting eye color is the sum of these effects.
Lens and eye size/shape aside, changing the amount of melanin *does* effect eye color, which we do see in a lot of cases. Eye color can change between infancy and older ages, as melanin production increases. Some peoples’ eye color even change subtly with the seasons, between summer and winter, as the amount of melanin they produce fluctuates.
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