ClipArt ETC
"A prism is used to disperse ordinary light, and slits are cut in paper S to only allow yellow and blue light to pass. These two simple colors will be blended by the lens, forming a light that is nearly white. The effect of mingling any two colors may be determined in this way." -Avery 1895

Color Spectrum

"A prism is used to disperse ordinary light, and slits are cut in paper S to only allow yellow and blue…