Ask Lena: CMKY vs RGB

October 4, 2010 / Updated: October 4, 2010 / Lena Shore
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Mixing Color with Light (RGB)

Mixing Color with Light (RGB)

What is the difference between are RGB file and a CMYK file? I understand the latter is needed to print, but what exactly is it?


The difference between RGB and CMYK is the difference between playing with flashlights and finger painting.


If you were to play with three different colored flashlights (Red, Green, and Blue) when you mixed them you would get these results:

  • Blue + Red = Magenta
  • Red + Green = Yellow
  • Blue + Green = Cyan
  • Blue + Green + Red = White

This is called additive color. This happens because white light contains the entire rainbow of colors. Putting light through a filter like a sheet of red plastic actually blocks out much of the color spectrum and leaves only the red. Rainbows and prisms work on the same principle. White light gets filtered through moisture in the sky (or cut glass) and breaks apart the color spectrum.

We use this technology all the time with computer monitors, televisions, mobile phones, and other devices that emit light.


Contrast to mixing color with light, if you were finger painting and using Red, Yellow, and Blue you would get these results:

  • Mixing color with paint

    Mixing color with paint

    Blue + Red = Purple

  • Red + Yellow = Orange
  • Blue + Yellow = Green
  • Blue + Red + Yellow = Black

This is called subtractive color. We are mixing the colors together and they darken and change. The pure (primary) colors we start off with are red, yellow, and blue. Secondary colors that come from mixing are green, purple, and orange.


Printing by it’s very nature is produced with paint (ink) on paper. So, professional printing (or your home printer) uses subtractive color.

Professional printing involves creating layers of  the pure colors plus black to create the rest of the colors. The press is essentially mixing the color on the paper as it prints.

Because the subtractive method tends to muddy colors, printers discovered they could change the formula a bit to get better results. By using cyan instead of blue, magenta instead of red, and adding black, (CMYK) they could get more professional and exact results.