Have you ever been asked that question? A naturopath from my old neighborhood asked me one day about my son who very often had “snot on his nose” as we say at home. For the life of me, I could no longer remember the color of his mucus, and yet I blew some!

Here are the results of my research on this very urgent subject:

Colors

Yellow: infection like cold or flu. White blood cells multiply to protect the body and color the mucus yellow.
green: purulent infection, white blood cells die off, and pigments in mucus are green
brown: dust or smoke inhaled.
Blue: bacilli
gray: cigarette smoke or air pollution
pink: asthmatics, blood cells.

I thought I had seen it all, but the blue and pink slime – a novelty!

In Summary

Color	Signification
Clear and translucent	The mucus is normal, so it is fluid (sometimes a little cloudy).
Yellow	This color indicates an infection. Leukocytes (or white blood cells), which increase when infected, stain the mucus yellow.
Green	It indicates that the infection is becoming purulent. This is because when white blood cells die, they release a green pigment.
Blue	This color is typical of a pyocyanic bacillus infection.
Brown	Brown spots may appear in the mucus from dust in the air you breathe or from smoke. But blood in the lungs or in the respiratory tract can also be the cause of these brown traces. The presence of blood is not necessarily a sign of seriousness.
Gray	Cigarette smoke or air pollution can cause gray mucus.
Pink	Les asthmatiques peuvent expectorer du mucus rose dû à des cellules sanguines provenant des parois des voies respiratoires.