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I've been reading about subtractive and additive color mixing and one thing is still confusing me. When I mix red paint, which reflects red light and absorbs all other light, with white paint, I get pink.

From what I read it almost seems like mixing white paint with red paint should result in red paint. Here's what I'm thinking: When two subtractive colors mix, their properties for what colors they absorb mix. White paint absorbs no light and reflects everything. Red paint absorbs everything other than red. When you add these hue's properties together for light absorption and reflection, you're left with the properties of red, essentially the lowest common denominator of sorts.

Where am I going wrong?

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As fixer1234 correctly explained, white is not simply "colorless" or "transparent", but it reflects light of all colors. By mixing pure red with pure white, you end up with 50% red light combined with 50% all wavelengths combined, which makes the red appear lighter (what we commonly call "pink").

There are 3 dimensional color systems like the Munsell color system that take the amount of light into account. It looks like this:

Munsell color system

  • The center top point (white) is an even mix of all wavelengths of light.
  • The center bottom point (black) is no light at all
  • The outermost points represent light of one single wavelength. This is the pure color.

Additive Color Mixing

If you shine a spotlight with a red wavelength filter on a white wall, you'll end up with a pure red color, like shown in the outer ring of the diagram.

If you dim the red spotlight (remove light), you make the red appear darker, moving towards the bottom of the diagram.

If you shine an unfiltered white spotlight at the same wall, you mix red light with white light, moving towards the top of the diagram.

If you put a wavelength filter of the color that's opposite of red on the second spotlight, you desaturate the color, moving towards the center of the diagram.

Substractive Color Mixing

If you put paint with a pure red pigment on a white wall, the wall (ideally) reflects only red light and absorbs all other wavelengths, like shown in the outer ring of the diagram.

If you mix the red paint with something that absorbs light instead of reflecting it (black paint), the wall reflects less of the red light, making it appear darker, moving towards the bottom of the diagram.

If you mix the red paint with something that reflects all wavelengths of light (white paint), the wall reflects all the red light and additionally some of all other wavelengths, making it appear lighter and moving towards the top of the diagram.

If you mix the red paint with the paint that is directly opposite in the diagram (green paint), both reflect a mix of different wavelengths, moving towards the center of the diagram. Red paint reflects only red light, but absorbs green light. Green paint reflects only green light but absorbs red light. The result is a mix of different wavelengths, but some of it gets absorbed, putting you in the center between black and white.

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  • Great answer, but you might also include how shining a colored light on a colored paint will react to make it a fully rounded answer. – computercarguy Feb 14 at 21:43
  • @computercarguy - except its not part of the question... – rebusB Feb 19 at 16:01
  • Great answer, but I think the idea that white paint is "all colors combined" is a little misleading. White paint is reflecting all colors combined, but is not itself made of all colors combined, that would result in black paint when talking subtractive colors. – rebusB Feb 19 at 16:06
  • I suppose now what's confusing me is the terms "additive" and "subtractive". Your two scenarios are explained in an almost identical way yet they're different things because one is light and another is a physical substrate. Light makes sense. YOu shine a light through a subtractive color filter, it REMOVES wave lengths thus resulting in a new color. I understand why that's subtractive. Where's the subtraction occurring with paint? – Scott James Walter Feb 20 at 12:16
  • @ScottJamesWalter You can compare paint to a color filter. In a ideal model red paint would remove any wavelength but that of red light, just like a red color filter would do. The difference between additive and substractive is the "stuff" you put on a wall to get white color. In case of light you put all diferent colors of light on a wall and the result is white. You need to add more light to get white, so it's called additive mixing. If you put all colors of paint on a wall, you end up with black. You need to substract paint to get a white wall, so it's called substractive mixing. – Elmy Feb 20 at 12:55
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The pink color of the mixed red and white is an optical illusion, similar to how inkjet printers create all the colors from inks of three primary colors by printing combinations of tiny colored dots close together.

The color in paint is particles of finely-ground pigments (colored powder), suspended in a liquid that dries into a film. When you mix red and white paint, you get a suspension of red particles and white particles. There is a mix of those particles on the surface of the paint.

The red particles reflect just the red light. The white particles reflect all the colors. The individual particles are too small to differentiate with the naked eye. What you see is a blend of the light reflected by the different particles on the surface.

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  • What exactly is the optical illusion you are referring to? – Joachim Mar 4 at 12:59
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    @Joachim, the optical illusion is that it appears pink but actually isn't. Under a microscope you would see red particles and white particles; there isn't really any pink there. The source of confusion behind the question is that if you uniformly mix colors, the red material "should" absorb the other light colors so there is nothing but red light for the white material to reflect. It's still a matter of how much of the other light colors the red material absorbs (it isn't binary for the whole material as was assumed). With paint pigment particles, it's easy to visualize why the amount matters. – fixer1234 Mar 4 at 17:46

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