I built a composting toilet on top of a 4 foot high two chamber system. The chambers were built in an E fashion with sheet metal door coverings.
I used cement blocks for the E construction and painted them with the clay soil around my property. What I did was dry the mud which is a burnt orange colour. When it was dry I manually sifted it through a flour sieve. The recipe for the paint is one part dry portland cement and four parts sifted mud dust. You don't need much as you think. You add enough water to make a paste and then you paint it on the blocks. My blocks have kept their colour for 10 or more years. From a distance it looks like Mud Bricks.