i have recently for the past 3 days been having a pure green stool, could this be colon cancer?

It is unlikely that green stools are a sign of colon cancer. Green stool is often caused by eating a lot of green vegetables, such as spinach or kale, or by taking certain medications, such as iron supplements or antibiotics. However, if you are experiencing other symptoms, such as abdominal pain, weight loss, or rectal bleeding, it is important to see your doctor to rule out any underlying medical conditions.