Usually, the mucus in your nose is clear. When you have an infection, your body sends in a bunch of white blood cells. These cells have an enzyme, or protein, that can turn your snot yellow or green. But some of those white blood cells are always there, so you may still have green snot if you aren't sick. A blackish color may be due to dirt in your nose. Red or brownish boogers can be from broken blood vessels. A small amount of blood is usually nothing to worry about, but if it doesn't go away, call your doctor.