The blue coloration of the iris is due to what?

The blue coloration of the iris is due to low concentrations of melanin in the stroma of the iris and because fibers on the fronter layer of the iris scatter and absorb some of the longer wavelengths of light.

Explanation:

Iris is thhe colored part of the eye and it is made up of two layers: the “back layer” called the pigment epithelium has brown pigment in it while the “front layer” or stroma contain overlapping fibers that might or might not have pigments in it (e.g. brown eyes have pigment melanin even in the front layer of the iris).

Eye color inheritance is a polygenic trait, meaning that it is controlled by the interactions of few genes.

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.