Out of the colors brown, green, white, red/bloody and black, green is probably the next to least worrisome:
5. brown - likely normal
4. green - rapid transit of digested materials (think post-drinking binge "loaf" here, or color of recent food intake
3. red/bloody: most likely hemorrhoids, but could also be a "tumah" in the large intestine that is either close enough to to anus not to be oxidized (black) or is bleeding rapidly.
2. black, tarry: likely blood somewhere between esophagus and beginning of large intestine.
1. white/gray: badness. potentially a tumor blocking the bile duct, which usually is in the pancreas.