I've had ulcerative colitis for 5 years. lately my stool is solid, dark brown and skinny. i feel good. but what does my stool say of my health?

Sounds healthy: Generally, solid, dark and skinny stool is suggestive of a healthy large bowel. This may be a signal that your bowel problems are under excellent control. Furthermore, that fact that you are feeling well supports this. If this is a drastic change from your previous bowel habits it would be prudent to discuss with your gastroenterologist.