Oh! I can imagine the scare you had from that red dye! I believe that can happen from eating alot of beets and eating red jello too.
Salads seem to be one of those things that can sometimes not cause problems, and other times cause diarrhea. The salads may have just got you spasming a bit. Hopefully it will calm down for you soon. Someone mentioned on another post that it helps to eat the salads with other food, to tolerate them better. Good luck.