Hi.
Thanks for your query.
The reasons for purple colored
scrotum with warm and rough skin after sex with your partner of 12 years can be:
Dermatitis due to excessive seating or so.
Another possible reasons can be an
allergic reaction to the retained chemicals in the form soaps or sprays like deodorants.
You might have rubbed the skin inadvertently.
Extreme temperature changes that you might have got exposed to.
I would advise you the following:
Clean the scrotal skin under plain water in shower or so.
Keep the area clean and dry and ventilated.
Consult a Dermatologist and get a prescription for an antihistamine and other medicines like
steroids if needed.
Do not apply anything to the area at home as changed character can make diagnosis and treatment difficult.
Wishing you all the best.