Here is what Dr Michael Tierra (herbal doctor/acu, ayurveda, western herbologist, etc. Author of some good books on self healing.) says about colonics:
Colonics are not for cold, deficient, weak individuals. The problems with water enemas is that they actually leave the colon drier. Injecting a quarter cup of sesame oil into the colon after an enema is balancing. [He is talking about both enemas and colonics.]
Interestingly, Traditional Chinese Medicine theory associates the large intestine with Kidney yang. It's as if one needs to retain some feces to stimulate and maintain lower warmer warmth. [Lower Warmer is a term used in Chinese Medicine. Western chronic conditions of adrenal fatigue, back pain, depression, hypothyroidism, kidney inflammation and sexual dysfunction parallel kidney yang .]
That being said, I have also seen and heard of some remarkable benefits from colonics. I think they are better done in warmer seasons.