Does green stool means cancer? i sometimes have this problem along with pellet like stool and constipation. does this mean colon cancer?

No: Color of stool is affected by your diet. It does not mean one has colon cancer. However, if you see bright red blood/bleeding in your stool- then you should see your doctor for more evaluation to see where is the source of the bleeding. You definitely need to make sure you hydrate ( drink water) yourself and increase intake of fibers to help your constipation.

Pellet stool: Maybe you are a llama, they have pellet stool ;). But on a serious note color of stool does not mean cancer unless thee is blood in the stool, and even then doesn't mean cancer for sure. If concerned see a stomach doctor ( gastro-enterlogist).

Just bile: The greenish color in stool is caused by the bile when it has not been in the gut long enough to go through a change to yellowish or brown triggered by gut germs. It is normal as is a loose consistency if it is greenish. Some digested material will take on a darker tint than others ; the germs in the gut will also impact the final product. I'd ignore the whole issue.

See below: For green stools, visit this site for info: https://www.mayoclinic.org/symptoms/green-stool/basics/definition/SYM-20050708 It is generally harmless. For constipation: You may take a fiber laxative like Metamucil and drink enough water daily so that your urine is colorless. For the long term you may try to increase your intake of fiber foods. Consult this site for fiber foods. http://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/high-fiber-foods/art-20050948