Sounds like mold, if so you need to ack quickly. If you have too much moisture you need more air movement, warmer temp, dehumidifier, somethin. Don't let good weed go bad.
Mold sucks! I've had 2 spots before while flowering. I prayed them with peroxide after removing the mold. In your case it sounds like it's too late for peroxide. I would definately raise the room temp and and get some air circulating there. Good luck.