Gunnar Svaetichin was a Swedish-Finnish-Venezuelan physiologist who, in 1956[1], showed by examining the external layers of fish retinas that electroretinograms display particular sensitivity to three different groups of wavelengths in the areas of blue, green and red. This provided the first biological demonstration in support of the Young-Helmholz trichromatic theory. He also gave name to the S-potential[2], which was the first experimental evidence that opponency existed in the visual system.
Jameson D., Hurvich L.M. (1982). Gunnar Svaetichin: man of vision. Prog Clin Biol Res., 13, 307-10.
http://www.hubel.med.harvard.edu/book/ch8.pdf
http://www.adsabs.harvard.edu/abs/1984Natur.308..360H
http://www.nature.com/nature/journal/v308/n5957/abs/308360a0.html
http://www.americanscientist.org/issues/id.841,y.2003,no.1,content.true,page.1,css.print/issue.aspx