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

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