Generally crohn's is more commonly found in the small intestine, when it's in the colon it's labelled as crohn's colitis because "colitis" means inflammation in the colon specificially and it's less common for CD to appear in the colon compared to the small intestine, so that is the only difference...of course different meds are used to treat CD affecting the colon (the same meds used to treat ulcerative colitis are generally used to treat crohn's colitis since UC is mainly a disease of the colon (but often with rectal involvement)...when you have crohn's colitis it's also more common for the crohn's to also affect the rectom and or the anus as well, but it's not written in stone either and as usual it varies from patient to patient....
When I first became sick with CD, it was affecting my anus (which is where it actually started, externally with perianal crohn's skin tags) then moved internally affecting my rectom, colon, and TI all at the same time for about
2 yrs before it finally subsided in the TI, but has remained constant in my colon and anus, on and off in the rectom.
There are 5 subtypes of crohn's disease, check out this link....
http://www.webmd.com/ibd-crohns-disease/crohns-disease/5-types-crohns-disease
Hope this helps!