Having green mucus that was another color before can usually be a sign that your infection is clearing up.
The mucus can turn green due to the immune system response fighting off the bacterial infection you have so having green mucus can be a sign that your infection is clearing up.
It's been my experience that when my mucus starts turning green the cold or other virus I have is getting out of my system and I'm usually beginning to feel better.
But if the mucus has began as green then it could mean you have an infection and you might want to get checked out by a doctor.
However most bacterial infections that lead to green mucus usually go away on their own within a week or two weeks without the need for antibiotics or other medical treatment.
Even eating some certain foods can lead to green mucus if you don't have a cold or flu virus.