Many different characteristics can be deduced from the color of one’s snot.

There’s a taboo against discussing issues like this, but we do it anyhow.
The noses mucous isn’t only there for show. Its color can tell you and your
doctor a lot about what’s going on in your body – especially when it’s been
an odd tint for an extended period.
You should know that snot color is not adequate to diagnose anything
outright.
Nonetheless, it provides a novel perspective on the unusual signals your
body sends when something is wrong.