: if colour is a spectrum going red thru purple then why do we have colours like magenta or pink, which seemingly connect purple back to red?


: if colour is a spectrum going red thru purple then why do we have colours like magenta or pink, which seemingly connect purple back to red?

In: Physics

Your eye has three types of color-detecting cells. Each has a color they’re most sensitive to: one is red, one is green, and one is blue. But they aren’t sharp, specific colors that they’re sensitive to, there’s some overlap. Yellow light, for example, is seen by both the red and the green cells. Which means that you can trick your brain into seeing yellow by mixing red and green light, like in a computer display.

For violet, the blue receptor does most of the work, but oddly enough the *red* receptor can also see things in the extreme edge of visible. So when violet hits your eye, the blue receptor and the red receptor see it.

Magenta is a strong blue plus a strong red, when adding light. It’s not a spectral color, it’s the mixing of two colors.

There are a lot of different pinks, some can have some blue in them and some are more accurately described as a pale red, which would be white (all colors) with some extra red.

Because our eyes and brain don’t directly detect the frequency/colour of light. Light is a continuous spectrum of wavelengths and our eyes have 3 types of cells (cone cells) which are responsive to different ranges of these wavelengths. These roughly correspond to red, green and blue light.

When the red cone is triggered we see red, when the blue cone is triggered we see blue. When all 3 are triggered equally we see white. If we send light of a wavelength between these regions then more than one gets activated. For example yellow light has a wavelength between red and green, so it triggers both cones and we see yellow. However we could achieve the same thing by using just red and green light to create the same response. This is why screens and cameras only need red, green and blue pixels to display all of the colours that a human can see.

Now consider what happens when we receive both blue and red light, both of the cones are triggered and we see magenta/purple. This means if you take the spectrum of light and imagine connecting it at both ends, the mid ground between red and blue will be purple.

There’s a difference between the possible colors that a single wavelength of light can produce (monochromatic light), and the possible colors that we can see.

You can mix “pure” colors of single wavelengths to make a new color that your eyes can see.

The single-wavelength colors make up the spectrum you described. The other colors are a mix.

The image below shows the colors we can see. The line around the outside is made up of the “pure” monochromatic colors. Draw a line connecting two of those colors to see what they can create when mixing.


Edit: Purple doesn’t connect back to red. The color wheel is a lie.

Magenta is an imaginary color – it’s the absence of green. It doesn’t exist as a wavelength of light the way other colors do. This article gives a pretty good ELI5 explanation:


The longest wave length we can see is red light. The shortest wavelength we can see is violet light, which we often call a shade purple but they are not the same. We can technically see a little beyond violet in to the ultraviolet range but most of this light is usually blocked somewhat by our cornea (lens) and so does not make it to our retina (light/color detector). People who have fake corneas from cataract surgery can sometimes see more of this ultraviolet light. This light is described as a bluish white color.

Just a note, black lights, also known as UV light look blue or purple to us because they produce a spectrum of wavelengths around UV and we are seeing those. We can also detect some of the intensity of UV light.

If the colors of light on the light spectrum were individual musical notes, then magenta is like a chord…multiple notes played together.