why purple is on the end of the rainbow/color spectrum

Question

First of all, I don’t understand why indigo and violet are split… why not just call it purple? Ok, not my question.

Colors of the rainbow all make sense to me except purple.

Red – orange – yellow…makes sense that orange is between red and yellow, and it’s the combination of those two primary colors, nice transition

This follows with green, blue. Green is between yellow and blue.

Now… if purple aka indigo and violet are a combination of blue and red, how can it be on the opposite end of red (very different frequency) and outside the frequency range of blue? I would expect a secondary color’s frequency to be between the two primary colors that create it

In: 76

Answer 1

Purple, or maybe more accurately magenta and pink, is our brain’s way of seeing the absence of green in the presence of other frequencies. We have three types of color sensing cells that get excited the most when light of a certain frequency hits them, they roughly correspond to red, green, and blue. Any color that consists of light at a single frequency will excite either red more than green more than blue (that’s how RGB lights can simulate yellow by emitting red and green, even though they don’t emit the yellow frequency at all), or blue more than green more than red, or green more than both blue and red. Magenta happens when blue and red are excited more than green.

So, when we look at the extreme ends of the spectrum, they look a little similar because neither end excites the green cells much.