When referring to mixing colors of light, specifically combining all the colors of the visible spectrum, the result is white light. This is due to the additive properties of light, whereby the combination of different colored lights results in a cumulative effect. Mixing shades of paint pigment, on the other hand, follows subtractive color theory, meaning the combination of all pigments would theoretically yield black. However, in practice mixing all paint colors does not produce a perfect black but more of a brownish color. The reasons for these differences have to do with the physics of light versus the chemistry of pigments.
Additive vs. Subtractive Color Models
There are two main color models that are important when considering mixing colors:
Additive
The additive color model refers to mixing colors of light. In this model, the primary colors are red, green, and blue. When you mix these colors together, they produce secondary colors cyan, magenta, and yellow. Mixing all three primary colors of light together produces white light. This is the principle behind how computer monitors, TV screens, and other displays produce color. The combining of the primary colored lights adds more wavelengths, eventually creating white light which contains all visible wavelengths.
Subtractive
The subtractive color model refers to mixing pigments or dyes, such as paints, inks, or other coloring agents. The primary colors in this model are cyan, magenta, and yellow, and the mixing of these primaries produces the secondary colors of red, green, and blue. Theoretically, combining all primary pigments should result in black, because each pigment absorbs certain wavelengths of light and subtracts them from the spectrum. However, in practice mixing all paint colors produces more of a brownish black rather than a perfect black. This is due to the imperfections and limitations of real pigments.
Light Physics
The reason that combining different colors of light results in additive mixtures and ultimately white light has to do with the physics of light itself. Light visible to the human eye consists of wavelengths ranging from about 400-700 nanometers. The specific wavelength determines the color perceived. Red light has the longest wavelength while violet has the shortest. When wavelengths are combined, the effect is additive, meaning if you mix red and green light, both wavelengths are present in the mixture and the human eye perceives this combination as yellow. Mixing all wavelengths together produces white light.
| Color | Wavelength range (nm) |
|---|---|
| Red | ~700-635 |
| Orange | ~635-590 |
| Yellow | ~590-560 |
| Green | ~560-490 |
| Blue | ~490-450 |
| Violet | ~450-400 |
Pigment Chemistry
Unlike light, pigments selectively absorb certain wavelengths of light and reflect the rest. For example, a red pigment absorbs blue and green light and reflects the red wavelengths, so our eyes see it as red. But real pigments are imperfect so a red pigment will not absorb 100% of the green and blue wavelengths. When you mix pigments together, each absorbs and subtracts certain wavelengths, and the combination produces a darker color. So theoretically, mixing all pigments should result in black, but real pigment mixes tend more toward brownish blacks. This has to do with the chemistry and microscopic composition of pigments. While combining paint colors produces darker browns, mixing printing inks can get closer to true black because the particle size is smaller and absorbs more light.
Practical Implications
The principles of additive and subtractive color theories have many practical applications in things like displays, imaging, printing, paint mixing, and more. Here are a few key implications:
Computer and TV Screens
Displays use the additive RGB (red, green, blue) color model to produce color pixels. Combining RGB at full intensity produces white light. Varying the intensity of each RGB primary allows displays to produce a wide range of colors.
Digital Image Processing
Digital cameras and image processing software rely on RGB color channels stored in pixels. Manipulating the RGB values allows adjusting the colors in images.
Printing and Graphic Design
The CMYK (cyan, magenta, yellow, black) color model is used for printing. The CMY primaries produce darker colors when combined. Black (K) ink is added for better contrast and true black coloring.
Paint Mixing
Understanding that paint pigments subtract wavelengths rather than adding them helps explain why mixing all paint colors produces a dark brown instead of black.
Stage Lighting
Combining RGB lights is used extensively in theater, concerts, and other staged productions to generate a full spectrum of colors.
Conclusion
In summary, mixing colors of light follows an additive model which results in combining wavelengths and ultimately producing white light when all primaries are mixed together. Mixing pigments, on the other hand, follows a subtractive model where each pigment absorbs certain wavelengths, resulting in darker browns when all are combined. The differences come down to the physics of light and the chemistry of pigments. Understanding these principles helps explain phenomena such as why computer monitors can produce white pixels but mixing paints does not make black. Having a solid grasp of additive and subtractive color theories has many applications in science, technology, art, design, and more.
