My tongue actually turned purple.
Due to my sickness, I didn't do my scheduled run tonight. Instead I opted for some yoga.
When deciding whether or not to run when you have a cold, the general rule of thumb is if the cold is from the neck up (ie a head cold) then you're probably ok to run; if it's from the neck down (ie in your chest and/ or lungs) rest. Generally running with a cold won't affect the severity of the cold and you'll feel better with a few endorphins in your system!
The other thing to watch out for is sinus infections. You don't want to run if you have a sinus infection - you'd probably make it worse and take longer to fight, especially if you run in cold, dry weather with one. If you feel pressure in your face/ sinuses, it's probably to take a rest day or two until you feel better, or check with a doctor.
Finally, DEFINITELY don't run if you have a fever. Running (or any strenuous exercise) will likely worsen your fever and other symptoms.
I will do another post on this topic at a later date.. Lots of interesting stuff, but I need to get some sleep to fight this thing off, I've got a half marathon to run!