Right on the border of Blue and Green. Wavelength approximately 495 nm. Well, there really is no good answer. But I found the idea of the physical center of the rainbow[1] intriguing, and none of the other answers even tried to look at it. read more
The interaction that occurs to create the primary rainbow will produce a spectrum of colors in order Red - Orange - Yellow - Green - Blue - Indigo -Violet (ROY G BIV) with Red occuring on the outside edge of the rainbow to Violet occuring on the insdie edge (closest to the center) of the rainbow. read more
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. read more