Can You Tell Me What Ingredient Is In The Red Coloring In The Cat Foods Ie; Friskies, Nutriplan Etc?

I am concerned because my maincoone cats are getting sick and vomiting it up after eating. I tested the therory by buying a brand without the red coloring on the food and during that time until the food was finished they didn't get sick. Then, I made an error, being in a hurry I ran in grabbed the bag of food. It had the red coloring in the food and then the cycle began again.