Page "Colloid" Paragraph 83

Thus, it has been known for many years that, due to repulsive Coulombic interactions, electrically charged macromolecules in an aqueous environment can exhibit long-range crystal-like correlations with interparticle separation distances, often being considerably greater than the individual particle diameter.

In all of these cases in nature, the same brilliant iridescence ( or play of colors ) can be attributed to the diffraction and constructive interference of visible lightwaves that satisfy Bragg ’ s law, in a matter analogous to the scattering of X-rays in crystalline solids.