My mucus is a deep yellowish green, did my cold give rise to a bacterial sinus infection?

Maybe: One of the common myths about the common cold is that any yellow or green mucous means there is a bacterial infection present. All viral upper respiratory infections (colds) can make yellow mucous even without bacteria. The predominant feature is time and change. If you have had a cold for longer than 7-10 days, or if suddenly you develop thicker mucous after seeming to get better, its possible.

It depends...: Many studies have concluded that the color of one's mucus cannot predict whether one has a bacterial infection or a viral infection. Statistically, most upper respiratory infections (uri's) are caused by viruses (the common cold). As a general rule, one should see a physician if your symptoms are progressively worsening.

Not necessarily: The association between the color of mucus and the presence of infection was removed long ago. Sinus infection would be defined by the presence of other symptoms - sore throat, headache, facial pains, earache, fatigue, chills, sweats, post nasal drip, achiness.

Maybe: You may have had your viral infection turn bacterial. The best way to find out is to have your doctor check you out. If it is only a very small amount of discolored mucus, it may clear on it's own, but if it has been going on for days, it is important to get it checked.