A normal color for bowel movements can vary quite a bit from pale yellow to dark green. Generally abnormal is considered gray or clay colored stools, and pitch black and tarry stools.
People with a very fast transit time (the time between when they eat and when they stool out that intake) may have stool that is relatively undigested. Mucus which is produced in the colon and rectum can appear light, but it is soft and resembles phlegm, not stool. Occasionally, a ball of stool may be coated with mucus and appear yellow-white-green. When it is submerged in water, the mucus will begin to disintegrate.
A truly light stool (all the way through) may indicate problems with the liver or biliary system, since it is the bile that colors the stool brown and green.