I think we will just go with watered down sour cream. The actor can control where the goop hits her (hidden by her purse) and it will read as goop on her. No color necessary. Then the other actors can eat real hummus. I will preset a film container in her purse. Am I thinking this out too much? Oh, yes! Hummus can stain! I will let you know if it works. Still willing to hear any other suggestions! Thank you!