system
Given the following post, respond as if you're commenting on Reddit:
human
What exactly determines mucus's color?
gpt
Basically the amount of cells and proteins present in the mucus.

Clear is just water and minerals whereas green would be chock full of immune cells and potentially even the pathogenic organism. Red to brown mucus would indicate blood.

And fun fact of the day: black mucus can be caused by bismuth sulfide, a Pepto-Bismol byproduct.