SHEARD, C. The Spectrophotometric Analysis of the Color of the Skin and the Observation by thisMethod in Normal and Pathologic Subjects. Archives of Internal Medicine. 1926, 38, 816-831
MACADAM, David L. Quality of Color Reproduction. Journal of the SMPTE. 1951, 56, 487-512
BUCK, G. E. Color Characteristics of Human Complexions. Illumination Engineering. 1948, 43, 27-49