Regarding the bright stool.....my son (4yrs) actually has experienced this a few times. This morning, he and his brother could be heard in the bathroom with gasps of amazement at the green poop. It was the reaction to the food dye in the frosting at the Big Y Thomas the Tank Engine cupcake he ate last night. The frosting is that crazy blue and the bile in the stomach reacts to it to make the poop green. Pretty gross.
Green stool is from green vegetables, some pop-sickles, colored drinks like Kool-aid, maybe from some vitamins, from iron pills...Please try to think what changed in his diet - it may just be some additive.
...or simply from fast food passage and consequently more unabsorbed bile in the stool. Does he drink a lot of fruit juices? Fructose, when in exscess can't be absorbed by a young intestine, so it drags water into intestine and causes diarrhea, but you say no diarrhea...OK, other causes of green stool/diarrhea are parasites giardia, bacterium salmonella and Clostridium difficile.