# Color mixing

Why when artists mix blue and yellow colors, we see green? What is the physical explanation of this?

mathman
Interesting contrast: mix red and green light and get yellow or orange.

Drakkith
Staff Emeritus
Why when artists mix blue and yellow colors, we see green? What is the physical explanation of this?

The combination of yellow and blue light stimulates the cone receptors in our eyes in about the same way as pure green light does.

See here: http://en.wikipedia.org/wiki/Color_vision

So there are three different types of vision receptors for the three basic colors (Young–Helmholtz theory). What must be the distance between two substances e.g. one blue and one yellow colored so we see it as green?

Drakkith
Staff Emeritus
So there are three different types of vision receptors for the three basic colors (Young–Helmholtz theory). What must be the distance between two substances e.g. one blue and one yellow colored so we see it as green?

I can't say since colors are subjective. There is no wavelength that we could single out and say, "This is green" or "This is blue".

sophiecentaur
Gold Member
2020 Award
So there are three different types of vision receptors for the three basic colors (Young–Helmholtz theory). What must be the distance between two substances e.g. one blue and one yellow colored so we see it as green?

There is a huge difference between how we can mix different colours of light (synthesis) and how our eyes actually analyse colours. The response of the eye is not really to three colours; the responses of the three sets of sensors are very wide band- corresponding to red(isn), green(isn) and blue(isn). A single monochromatic source may well stimulate all three sensors. However, it is possible to mimic the perceived colour of an object by using three, very narrow band, sources. The three (RGB) phosphors, used in colour TV are narrow band (as narrow band as is compatible with making them bright enough, actually). To sum up - analysis is broadband and synthesis is narrow band.

The above quote, refers to subtractive mixing of colours, using pigments or filters, which is totally the inverse of mixing colours using light sources. Pigments work by absorbing certain colours. Mixing two colours of pigments will produce a result which only lets through or reflects wavelengths that the two pigments will each let through. Printer inks (Magenta, Yellow and Cyan) are usually thought of as 'Minus green', 'Minus Green' and' 'Minus Blue' and 'Minus red', respectively. (Or R+B, R+G, or B+G)

Or are you referring to the spatial discrimination / acuity of the colour receptors on the retina?

Also, incidentally, a grid of blue sources, interspersed with yellow sources will look white (or, at least, neutral grey) because Yellow corresponds to R+G and White corresponds to R+G+B.

sophiecentaur