The great thing about egg tempera in artwork is that you can use almost anything to make pigment. Tempera artists often grind and mix their own pigments. The egg acts as the binder, and will stick almost any pigment to many different surfaces.
( What the Masters probably did not
know, is that heating egg yolk to 63 Deg. C for 2-3 minutes, greatly
increases the emulsifying properties which enhances the paint flow and
appearance when dry.)