There's something I have to get off my chest. It's been bugging me since 1988 or so when it came up as a trivia question in grade 8.
There is no indigo in the rainbow.
The grade 8 trivia question, with a Twix bar on the line, was: "How many colours are present in a rainbow?"
If we were to discuss the number of colours present in the rainbow, we would have to set some kind of standard for how precisely we want to define a colour. In reality, we have to admit that for all practical purposes there are an infinite number of colours present in the rainbow.
So we need to set a limit.
We could argue that the limit is "primary colours", in which case we have 3: red; yellow; blue. All other colours can be defined by mixing these three together. Your monitor, of course, use three different colours: red; green; blue.
Now we could also argue that we ought to count secondary colours as there are enough obvious colour changes for the human eye to pick up. In that case we have: red; orange; yellow; green; blue; purple (sometime called violet for no really good reason).
Fine. That makes six colours and I could completely understand that.
But SEVEN colours? What would the seventh be?
Indigo? Are you on crack? Indigo is just a colour defined halfway between purple and blue. Why on earth would you count that?
If you're going to argue that purply-blue (indigo) counts, then I would have to argue that bluey-green (teal?) should count. How about reddy-orange (peach?) or yellowy-green (puke green).
Indigo is a crock. Indigo is a scam. Drop it from the official colours of the rainbow forever and never look back.
All I'm saying is that someone owes me a Twix bar with two decades of interest.