The Colours of the Rainbow:
RED – ORANGE – YELLOW – GREEN - BLUE – INDIGO - VIOLET
From a physics point of view, the rainbow spans a continuous spectrum of colours—there are no "bands." Newton originally (1672) named only five primary colours: red, yellow, green, blue and violet. Only later did he introduce orange and indigo, giving seven colours - by analogy to the number of notes in a musical scale! (I have to say, I always had difficulties identifying “indigo”.)
I also have a Rainbow post at my other blog today – The Island of the Voices. There you can read a bit about mythology and folklore connected with rainbows; and also about the phenomenon of the double rainbow.