Welcome to the STD forum.
No STD behaves this way or looks like you describe, so definitely no worries there.
It seems the
spotBirthmarks - pigmented
Liver spots
Measles, koplik spots - close-up
Mongolian blue spots is most prominent at times of
maximumMaximum strength decongestant
Maximum strength wart remover blood flow to the
penileCancer - penis skin, as occurs during sexual arousal, or in the morning following a nocturnal erection. This strongly suggests something related to the blood vessels in your skin. My guess is you have a hemangioma, sometimes considered a kind of mole. Hemangiomas are entirely harmless, really just a normal variation in the skin. But to be certain, see a health care provider, preferably a dermatologist. Even when you are not aroused, a hemangioma probably would be apparent to a dermatologist on careful examination. In the meantime, don't worry about it, and stop getting tested for STDs.
Good luck-- HHH, MD