What is the red fire retardant used to put out wildfires made of?

One material is called Foscheck. It's made up up of 85% water, 10% fertilizer (ammonia phosphate and sulfate ions), and 5% other ingredients (iron oxide for color, clay, or bentonite). It works by coating everything with the sticky moist mixture. It is colored red to make it easy to spot from both the ground and the air.