A rainbow is composed of the entire spectrum of colors of visible light, from the longest wavelength, red, to the shortest wavelength, violet. The order of colors in a rainbow is easiest to remember by the following mnemonic (a formula that helps one remember something): ROY G. BIV. R=red, O=orange, Y=yellow, G=green, B=blue, I = indigo, and V=violet. Red is at the top edge of the rainbow and violet is at the bottom edge, with the other colors in between. http://www.help619.com