When you have a cold, it seems like you produce more mucous, but the mucous really just changes consistency and becomes thicker and often a different, greenish color.
The reason that the mucous during a cold becomes green later in the course of the cold is because your immune system sends white blood cells called neutrophils rushing to the lining of the nose to try to fight infection. These cells contain a greenish-colored enzyme, and in large numbers they can turn the mucus the same color of green.
Healthfacts.blog 