So where does Indigo come from?

This morning I woke up before 4:30 to drive Kevin to the airport.

On the way back I had a realization about the order of the colors in the rainbow that I had never noticed before (don't laugh at me):
ROY G. BIV

Red is first and then Yellow is third; Yellow and Red combine to make Orange, the color between them. After Yellow, the next primary color is Blue. Blue and Yellow combine to make Green, the color between them. After Blue is the mystery Indigo, I'll skip that, but then comes Violet- the color that Blue and Red combine to make- and looping back around, Red comes after Blue.

WOW!

Now how have I never ever noticed that before?