Jun 22, 2015
Two pigments, brown protoporphyrin and blue biliverdin, are all that are necessary to cover all of the naturally occuring range of color in birds’ eggs. This was demonstrated with computer modelling of the resulting color from mixing of the two pigments combined with the reflectance of the egg shell surface. This range is represented as dots in the tetrahedron with short, medium, long, and ultraviolet wavelengths at the points due to birds having 4 types of cone cells specialized for their respective wavelength ranges. Examples of eggs across the color range are numbered 1 through 5.
http://www.audubon.org/news/cracking-code-egg-coloration
http://rsbl.royaocietypublishing.org/content/11/5/20150087