The Orange Man was a clinic patient who came in complaining of a sore back, but really he was orange.
He came into the clinic claiming that his back had become sore while he was golfing. House told him that he was orange and apparently he had not noticed. House also told him that his wife is having an affair because it was one thing that he hadn't noticed that he was orange, but if his wife hadn't noticed than she must not have been paying any attention. He came back to the clinic once more, him and his wife had apparently gotten a divorce because he no longer had the ring on his finger that (or he's taken the ring off to see if his wife is really ignoring him as much as House says) he had during his first visit so House was probably right about the affair.
He diagnoses the orange skin as being caused by eating too many carrots turning him yellow (due to excess of carotene, a natural dietary pigment), along with Niacin (Vitamin B3) turning him red.
After that, the man complained to Cuddy but she didn't do anything about it.
He was also House's first clinic patient who returned to the clinic after refusing to work in it for six years.