My son had what they call a hydrocoele, which is basically a fluid hernia in his testicle. It happens when the testicles drop from the body but the hole doesn't close up. His pediatrician noticed it around 1 year. I hadn't noticed anything, nor had a previous medical staff. We watched it for a year and it didn't go down on its own, as we hoped, so my son had minor surgery to close the hole, done by a pediatric urologist. He's fine now. His main symptom was swelling. It never turned colors though. I would have him checked ASAP, even if you have to go to the ER.