Im 35 years old, ex-smoker, i have changing stool, sometimes pale, sometimes green, sometimes dark, sometimes loose, i have ab cramps and aching joints. i have gassin?

Gallbladder?: Gallstones could cause abdominal discomfort and stool changes. Intolerances to certain foods (gluten, dairy, etc) can cause bloating and loose stools but usually not color changes.

Colonoscopy: Color other than back should not take seriously. Even black can be somewhat ignored if taking peptones-bismol. The changes in bowel habit would be somewhat disturbing. Ask pcp what he/she thinks about a colonoscopy.