Fecal boluses will be of different colors according to what they are composed of, obviously. So we will think about what one has eaten, and we will think about what the body has done with it. Color is a pertinent quality of food, feces, faces, and on, because it tells us something about the constitution of the bearer. Humans are sensitive to color, I'll argue, because it has been adaptive to be so, because of its diagnostic quality. Therefore, it is a good idea to consider the color of our feces.
The liver provides bile (dark greenish in color) for the dissolving of lipids in the digesting food. This green color is a major provider of tone in feces, and if feces are rushed through too rapidly, as in the case of diarrhea, they will come out with a greenish color.
The second major contributor to color is yellowish bilirubin, a break-down product of dead red blood cells. Bilirubin can make that yellowish color around the edges of a bruise and it adds to the bile coloration to make the typical brown of feces.
Foods that don't get entirely broken down due to high fiber content may also contribute to color, such as nuts, beans, corn, and red pepper. Beets, taken in sufficient quantities, will lend quite a bit of uniform red color to feces and urine, not to be mistaken with blood.
Blood in the feces will add its color, and is reason to seek medical attention. Interesting to note, as we consider the color of feces, that in less developed, particularly tribal civilizations with high parasite burdens, bloody diarrhea is considered standard state. Parasites, such as pieces of worm, may be visible in the feces. Parasite eggs in the feces is a quick diagnostic device.
Darker feces are indicative of greater water retention; the large bowel absorbed less water from the fecal bolus.
Feces leaving the body have the diagnostic advantage of having been through the entire alimentary system, and bear traces of the mouth, stomach, bowels, and colon. We can use our keen attention to color as indicators of health everyday.