Oregano Turning Black upon Harvesting

Why does Oregano turn black upon harvesting? It appears to do so where it was touched by the hands doing the harvest. Is it a fertility issue? Also, what is the proper post-harvest temperature for oregano? I see very conflicting answers.

This may be a problem of too high humidity when the oregano is drying. Bacteria transferred to the plant during handling get a chance to attack the plant when the humidity is high enough. Bruising makes the tissues more vulnerable too. Try drying the plants in front of a fan or place them into a very slightly heated oven with the door ajar.