In the first layers we start with thick color, to create a solid foundation. Then, without covering all of the surface, we continue with thinner and thinner layers created with a mixture of the egg emuslion and some water. Thin layers allow light to penetrate. Thus the different layers interact with each other creating a new color.

The same goes with the colors themselves: The juxtaposition of warm base with cold highlights, creates  an impression that resembles silk. In this case, egg tempera -that works magnificently with cold tones (it is true that warm tones of eggtempera is not as rich as oils)- gives the shine and movement of sizzling silk on garments. That is the so-called “Silk effect”

More info on color layers, on this blog? Just try https://angelicon.gr/color-recipes-in-byzantine-iconography/

There are many interesting artices on colors and their use, a very interesting one is : https://www.coloracademy.co.uk/ColorAcademy%202006/palettesandmixing/ancient/europe/greek/front.htm