Thursday, May 01, 2008

There's no Indigo in the Rainbow

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.

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.

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3 comments:

Mary said...

Follwed you over here from the J&G...The indigo thing also kind of annoys me too. There are an infinite number of colours in the rainbow, not including the ones you can't see with the naked eye. Technically, the primary colours of a rainbow (being that it's made of light) are red, green, blue but then, I guess you'd have to assume that the rainbow in question was an actual rainbow and not a picture of a rainbow or some other such nonsense. As for the purple thing, my high school art teacher always claimed that violet was the name of the colour and that the term purple was invented by Crayola. I have no idea if it's true or not but there it is.

Greg said...

Glad to see I'm keeping some of my loyal readers. I'm always heartened to hear from you.

According to wikipedia (which quotes the OED), "purple" was a word used as far back as AD 976 ... predating Crayola somewhat.

I think RGB is used because those are the three colours that our eyes best sense. The actual light itself just comes in at a wavelength and a brightness. It's not really composed of other wavelengths.

Anonymous said...

I totally agree. We wouldnt put red, redorange, orange, orangeyellow, ... We sholdnt put indigo in there! I so agree!:)