Hi,
When you have fever, NEVER train, and when the fever is gone, don't train intensive for the double of the time you got fever. So 2 days with raised temperature equals 4 days of not intensive rides. The reason for this: the possability of myocarditis: inflamation of the heart.
Then with a cold: as long as it's above the shoulders, and you feel well enough, you could train light, not too intense.
A light recovery training is sometimes better than keeping the bed.
Good luck
Bart