I have UC and find fiber is not my friend when the disease is active. Also, beans/legumes, grains (except white rice is ok), but I don't have trouble with greens.
My suggestion is to go to the diet that you do best on, as limited as you can live with, start with just a few non-reactive foods, then add a food every 2 weeks or so (give your body time to react) until you can pin down what does not agree with you. I have an uncle who also has UC and his tolerances are different than mine. He has trouble with drinking alcohol (of course he does drink way more than I do so it may be a quantity issue here) both of us have had the most trouble with a strict vegetarian diet.
I assume you are in communication with your doc and are taking medication as well (sometimes there is a definite place for conventional medicine)