+1 for the strict adherence to zone 1 while sick, if you ride at all. Just take it easy and you'll feel better faster.

Also, there's absolutely nothing that you can tell from the color of mucus.

It's true that the VAST majority of sinus problems are viral in nature, and symptomatic treatment is the way to go (decongestants, etc.). For riding I've found that I get some killer headaches and my HR gets higher than normal when I take Sudafed, and I get more dehydrated with decongestants, so I like to stick with non-systemic treatments like Afrin.

Even with bacterial sinusitis, a lot of cases get better on their own without antibiotics, but if you keep having pain in the sinuses (try pushing on the bones just below your eyes (maxillary sinus), the bridge/root of the nose between the eyes (ethmoid sinus) or the bony part of your brow (frontal sinus)) that isn't going away with decongestants and lasts more than a few days, you should really see a doctor. Also, if you're having fevers/shaking chills/etc., see a doctor because it may be more likely a bacterial thing, especially if you have fever spikes.

Basically, anything that doesn't behave like a cold should, i.e. gone in about a week without antibiotics, you should see a doctor.