My testicles have a dark patch under them and they look irritated and red a little (im a 23 african american male)?

I believe that you're describing discoloration of your scrotum. Friction & moisture can cause this. Try avoiding tight jeans, wear white cotton underwear, keep your groin & scrotum clean and dry. See your MD if not improved.

You mean the skin- as the testicles cannot be seen from the outside. Try cortisone cream for a few days . If not better you need to be seen by an MD/Urologist for proper diagnosis and Rx