Roy G Biv is a memory aid used to recall the order of the colors of a rainbow or the rainbow pattern (spectrum) created when a prism breaks up white light by refracting different wavelengths (colors)...
The fictional "Roy G. Biv" is the acronym mnemonic for the 7 colors of white light, in order of their wavelengths from shortest to longest :
Red, Orange, Yellow, Green, Blue, Indigo, Violet = ROYGBIV...