system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is hypopigmentation associated with blue eyes, when the complete lack of pigment in albinos causes red eyes?

As the title says, hypopigmentation in humans is ordinarily associated with **blue eyes**, as well as light skin and blond hair.

However, albinism, the complete lack of pigmentation, while being associated with most of the same phenotypes, just to an extreme degree, causes **red eyes**, not blue eyes.

What is the explanation for this apparent discontinuity in iris colour?
gpt
Regardless of our skin/eye/hair color, non-albino people have black pupils because the insides of our eyes have pigment to prevent light from bouncing around. The type of pigment and amount may vary based on our genes but it's enough to keep our pupils black. Extreme amounts of light from say a camera flash can exceed the light absorbing ability of our eyes, making us have red pupils in photos.

Albinos lack this pigmentation so the insides of their eyes don't absorb as much light. This causes light to light up the inside surface which is full of blood, making their pupils look red in normal lighting conditions.

Albinos typically have blue irises due to the lack of pigmentation.