Helmholtz, H.  Handbuch der Physiologischen Optik (1867).

One of the most important works on physiological optics.  The most significant passage contains what has become known as the Young-Helmholtz theory of color sensation.  Helmholtz presents his experiments which modify Young's work and substantiate his formerly repudiated claims about tri-color vision.  Moreover, Helmholtz extends the theory to explain red color blindness.     

Hermann Ludwig Helmholtz (1821-1894), German scientist and surgeon,  made fundamental contributions to the fields of physiology, physics, optics, mathematics, meteorology and thermodynamics.  He is best known for his statement of the law of the conservation of energy.  His exhaustive physiological studies in the field of optics resulted in this work and the invention of the ophthalmoscope and the ophthalmometer.

Thomas Young (1773-1829), English physician and natural philosopher, made many discoveries in the fields of physiological optics, physics, natural philosophy, and the study of Egyptian hieroglyphics.   He became famous for establishing the principle of light interference, which determined the wave nature of light.  While applying his wave theory to color sensation in the eye, Young conjectured that all color sensations, aside from the three primary sensations of red, violet, and green, are physiological mixtures of the three primaries.   His scientific peers, however, did not readily accept this theory of tri-color vision. 

(Sources: Garrison & Morton; Encyclopedia Britannica; Dictionary of Scientific Biography)