Okay,
I am going to go out on a limb and say that the formula probably has nothing to do with the colitis. I have, IBS, Colitis, and Chron's disease, nothing of which was CAUSED by the food I ate. No one knows what really causes any of these chronic illnesses. Their, and my best guess is a combonation of stress and genetics. Look to the family for other cases of digestive disorders, the three of which I have is a good place to start.
I am sorry he has been diagnosed with this at such a young age. It will be a difficult time for him especially as a child. You will need to find the foods that aggrevate it. With everyone it is different. Basic set offs are milk/dairy, seeds, and food allergies. So the next step, for me, would be to go to an allergist and have him tested for food allergies. This will not cure the colitis, but will help keep it from flaring up.
As far as the current flare up, you may want to cause him the least stress possible. Try not to be stressed around him, no fighting around him. Try to keep him on a schedule so he knows what to expect and is not stressed out by things. I know it sounds ridicuolous, but stress is one of the biggest triggers of any gastro illness.
If you need further info, I will share my course of treatment with you, just reply.
Good luck, and I wish the little guy the best of luck.
L.