What happens when two colours overlap?

Venn diagram 1: yellow + pink = peach

The world in venn begins with a simple idea — what do we get when we mix two colours?

Is the outcome a child of the two colours, containing traces of both, or is it a new colour altogether? To find the answer we first need to understand what colours are.

“Colour derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors. By defining a color space colors can be identified numerically by their coordinates.
Most light sources emit light at many different wavelengths; a source’s spectrum is a distribution giving its intensity at each wavelength. Although the spectrum of light arriving at the eye from a given direction determines the color sensation in that direction, there are many more possible spectral combinations than color sensations. In fact, one may formally define a color as a class of spectra that give rise to the same color sensation.
For example, most computer displays reproduce the spectral color orange as a combination of red and green light; it appears orange because the red and green are mixed in the right proportions to allow the eye’s cones to respond the way they do to the spectral color orange.” — Wikipedia

How does any of this even matter? What are the practical applications in life? Imagine you have blond hair and would like to colour it pink. As we can see from the diagram above, adding pink dye to your hair would make it peachy. To get pink as the end result, you should instead use a magenta dye.

Venn diagram 2: yellow + magenta = pink

It is interesting to note that the RGB values of the overlap area are an exact average of the two circles’ colours. In this sense, the overlap colour is a child of the two parents, bearing traces of each.

This image (when viewed in full size, 1000 pixels wide) contains 1 million pixels, each of a different color. — Wikipedia

As the human eye can distinguish about 10 million different colours, the shade born of the overlap can also be considered a new colour, just as every child is unique.

There are many other factors such as surface/device properties and lighting that determine how colours interact and how we perceive them. Although the pink is the same in venn diagrams 1 and 2, it appears more peachy in 2 when juxtaposed with the stronger magenta.

Another important consideration with colours is whether they are additive or subtractive. Additive colours refer to light sources such as the screen you are reading this from.

Additive color mixing: adding red to green yields yellow; adding all three primary colors together yields white. — Wikipedia

Subtractive colours refer to the way surfaces absorb some wavelengths of light, and bounce off others into our eyes — resulting in the colour we see. The example of the hair dye is a subtractive process and should be translated into CMYK — a different colour coding system that is used to describe inks and pigments.

Subtractive color mixing: adding magenta to yellow yields red; adding all three primary colors together yields black — Wikipedia

What are your thoughts on mixing colours and do the results ever surprise you?

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