Skip to Content

Does red and green make gray?

Color mixing is a fascinating topic that many of us experimented with as children. Who doesn’t remember eagerly combining paints or crayons to see what colors emerge? As we grow older, we gain a more sophisticated understanding of color theory and the physics of light that determine what happens when colors mix. But some color combinations continue to puzzle us. One that often crops up is: what happens when you mix red and green? Does combining these vivid primary colors produce gray?

The Basics of Mixing Pigments

When working with paints, dyes, inks and other pigments, the colors we see result from light being reflected back to our eyes. For example:

  • Red pigments absorb blue and green light, reflecting back only red.
  • Green pigments absorb red and blue light, reflecting back just green.
  • White pigments reflect back all colors of light equally.

So when painting or printing in full color, mixing two pigments means combining their reflective properties. Red and green pigments mixed together will reflect back red light as well as green light. Our eyes and brains interpret this combination as a yellow color.

The RGB Color Model

Things get more complicated when working with light directly in additive color systems like computer monitors and projectors. These devices use red, green and blue (RGB) lights to create the colors we see. The RGB color model works differently than pigments:

  • Red light shown with green light makes yellow light.
  • Red light shown with blue light makes magenta light.
  • Green light shown with blue light makes cyan light.

So in additive RGB systems, combining pure red and pure green light does not make gray. Instead, it makes yellow, just like mixing red and green pigments.

Perception of Color Mixing

Our perception of color mixing is strongly influenced by contrast and surroundings. For example, a small patch of yellow will appear vivid and saturated on a white background. But viewed against a range of rainbow colors, that same yellow may look dull, dark and grayish by comparison.

This effect is heightened when mixing light vs pigments. Adding red light to green light yields a bright, intense yellow. But mixing red and green paints produces a far more olive, earthy yellow. This difference comes down to the intrinsic properties of light vs reflectance. Mixing lights multiplication combines intensities, yielding brighter results. Mixing pigments averages their reflective properties, resulting in darker mixtures.

The Special Case of Red, Green and Blue

Red, green and blue are the primary colors of additive color mixing. This means that in theory, combining red, green and blue light in equal proportions should produce white light:

Color Amount
Red 33%
Green 33%
Blue 33%

However, in practice this balanced combination often ends up looking more like a light gray or off-white. This is partly because true primary red, green and blue are difficult to produce. Small imbalances in the component colors shift the result away from a pure white.

Nonetheless, combining red, green and blue light in roughly equal amounts can produce a light gray color. Although not a true achromatic gray, it appears desaturated compared to the vivid component colors.

Mixing Paints vs Light

As we have seen, mixing colored lights and mixing pigments follow different rules. We can summarize the key differences:

Mixing Type Rules Red + Green
Pigments/Paints Reflectance is averaged Makes yellow
Light Intensities are multiplied Makes yellow
Light (RGB) Unique primary colors Makes desaturated gray

This explains why mixing red and green paint, or shining red and green spotlights together, makes yellow. But carefully balancing red, green and blue spotlights or pixels can generate a neutral gray color.

Light vs Pigment Gray Mixing

True achromatic grays can be achieved with paint mixing because pigments work by subtraction. Combining all paint colors to block full-spectrum light reflection will make a dark gray or black, depending on consistency:

Color Amount
Red 33%
Green 33%
Blue 33%

With light mixing, grays are possible by carefully balancing the primary RGB colors. But it’s easy to be off-balance and end up with a faint tint:

Color Amount
Red 30%
Green 35%
Blue 35%

As demonstrated above, even slightly unequal amounts of red, green and blue will prevent an accurate neutral gray.

The Takeaway

Does combining red and green make gray? In summary:

  • Mixing red and green pigments makes yellow, not gray.
  • Mixing red and green light also makes yellow.
  • But red, green and blue light mixed together in roughly equal amounts can create a near-gray.
  • Accurate achromatic grays are best achieved by mixing all pigment colors.

So while red and green alone won’t make gray, the special primary properties of red, blue and green light can produce a workable, desaturated neutral when carefully combined. The mixing of color is complex, but illuminates both physics and perception.

In summary, mixing pure red and green colors will not directly produce a gray color. However, by understanding the different additive and subtractive color models, we find that combining the primary RGB colors in light can generate a near-neutral gray under the right conditions. The intricacies of color theory reveal as much about human vision as the physics of light itself.