Color Mixing
Why does mixing red and green paint make brown, while mixing red and green light makes yellow? Drag the circles to explore the fundamental difference between additive mixing (light, screens) and subtractive mixing (pigment, print). Click anywhere to read the color values.
About this experiment
The distinction between additive and subtractive color mixing reflects two fundamentally different physical processes. When colored lights overlap, their wavelengths add together — your eye receives the combined energy of both sources. Red light plus green light stimulates both the red and green cone cells in your retina simultaneously, producing the sensation of yellow. Add all three primaries (red, green, blue) and every cone type is fully stimulated, producing white. This is additive mixing, used by every screen you look at: each pixel is a cluster of tiny red, green, and blue sub-pixels.
Subtractive mixing works in reverse. Pigments and inks absorb (subtract) certain wavelengths from white light and reflect the rest. Cyan pigment absorbs red light; magenta absorbs green; yellow absorbs blue. When you mix cyan and yellow paint, the cyan removes red and the yellow removes blue, leaving only green wavelengths to reach your eye. Mix all three subtractive primaries and, in theory, all light is absorbed — you get black. In practice, real pigments are imperfect, so printers add a true black ink (K), giving us the CMYK system.
The science of color mixing traces back to Thomas Young's 1802 trichromatic theory, refined by Hermann von Helmholtz and James Clerk Maxwell in the mid-19th century. Maxwell produced the first color photograph in 1861 using three color-filtered exposures — an additive process. A subtle consequence of our three-cone vision is metamerism: two surfaces can look identical under one light source but different under another, because they reflect different spectra that happen to stimulate your cones equally in one case but not the other. Every color match your monitor makes is technically a metameric trick — it produces the right sensation with entirely the wrong wavelengths.