Q: normal after diarrhea?

my puppy had pretty bad diarrhea yesterday. explosive, even. the vet told me to feed him chicken and rice. he didn't seem too interested in eating it yesterday, but ate all of the chicken and some of the rice today. he pooped today, just a little bit, but it was on the road to being solid again. my concern is that it was mixed with a mustard-y discharge. it was pure liquid. there doesn't seem to be a change in his personality, so should i be worried? does anyone know what the yellow stuff might be?