Refractive index of milk: The refractive index of a solution is dependent on the refractive index of the solvent (in this case water at ~1.330) and the particles in the solution. Milk has a refractive index of ~1.338. Casein micelles are the primary contributors to the higher refractive index of milk compared with water. Light scattering in milk is caused by particles of relatively large size whose refractive index differs from water. In this case, light scattering by fat globules and casein micelles are the primary contributors to the color of milk. Whey proteins are too small in size and leukocytes (somatic cells) are too low in concentration to contribute substantially to light scatter in milk. The carotene in fat globules scatters yellow light and is responsible for the yellow color of cream. The size of casein micelles results in preferentially scattering of blue light more than red light, hence the bluish tint to skim milk. Milk whey (serum phase) contains riboflavin which gives whey its yellow-green color