I wold give him chicken and plain boiled rice only until any current bout of colitis is sorted out. After that, I would have a word with your vet about putting him on a Prescription Dried or Tinned Food (Vets usually prescribe Hills) for dogs with sensitive stomachs.
Dont give him treats with any flour or sugar or biscuits, etc. made for humans.
Chicken and rice is very good, but long term that alone would not give all the nutrients he needs.
(We had a dog that suffered from colitis and lived to the good age of 15. She only ate Chappie. The vet said that Chappie, even though it smells foul, is one of the best dog foods available and it has a high content of cereal, and it is certainly not expensive.
Try and avoid the richer dog foods like meaty chunks in gravy etc. They will upset him tum.
Hope you sort it out, Bobby