If you read your "owner's manual", you will see that we were not genetically designed to eat grains and sugars. Our genes code us to eat lots of greens, animals that eat greens (not grains), the eggs of animals that eat greens, seeds and nuts, and plenty of clean water. That is it. That is your genetic code diet. I would also reduce the intake of nightshade vegetables (tomatoes, white potatoes, eggplant, and peppers).
Simply cutting back your intake of grains (wheat and gluten products) and sugars will go a long way to help your digestive system heal. A diet plentiful in vegetables and fruits is critical, except for the nightshade group. Probably one of the most important steps to take if you suffer form colitis is to take a good from of probiotics: re-populating your bowel with healthy cultures of friendly bacteria. Eating fermented foods (ex. sauerkraut, kimchi) is an excellent source of probiotics.
Another important ally to healing is to optimize your intake of vitamin D and omega-3 fatty acids (krill or fish oils). Avoiding stimulants and irritants are also key (caffeine, aspirin).
Lastly, exercise that increases your circulation activates healing and well-being. I like interval training and body weight exercises because they are easy to perform, are efficient, effective, and inexpensive.
In summary, eating what we are genetically designed to eat, adding some assistance to digestion and healing in the form of probiotics, optimizing your vitamin D and omega-3 fatty acid intake, and exercise are all great steps to take to heal your digestion.