How come there's no all 7 colours of the actual cầu vồng on a LGBT cầu vồng Flag instead of only 6? I'm just curious that's all. Does anyone know for sure the right answer to this simple câu hỏi of mine?

What ever happened to the last colour, colour indigo? It supposed to be the colour of the last stripe on a cầu vồng Flag. Where did it go & how come the 7th colour of a real cầu vồng somehow has managed to get Mất tích since it was created back in 1978?