system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What exactly causes snot to be green/yellow when one has a sinus infection?

It just seems like a silly color. Neon green doesn't exist that often in nature.
gpt
Bacteria can be all different colors, but because they're so small, it's only obvious when they're in large groups. That's also why if your nose is running from just allergies or a viral infection, it tends to be clear - few or no bacteria means no color.

Color can actually be used to help identify bacteria - generally, yellow is *Staph. aureus*, green is *Pseudomonas* and white is *Strep.* There's even a bacteria used in microbiology classes that's bright red, called *Serratia marcessens.*