Red, green, and blue are known as the primary colors of light. When you mix different amounts of red, green, and blue light together, you can create all the other colors that make up the visible light spectrum. This is known as additive color mixing, and it’s the principle behind how color televisions, computer monitors, and other digital displays create different colors. Understanding what happens when you combine red, green, and blue light gives insight into the nature of color and light itself.
The Primary Colors of Light
Red, green, and blue are called primary colors because they cannot be created by mixing other colors together. Instead, all other colors can be formed by combining red, green, and blue in different proportions. For example, mixing red and green light makes yellow light. Mixing all three primaries together equally produces white light.
The primary colors of light are different from the primary colors of pigment, such as paints and inks. With pigments, the primary colors are cyan, magenta, and yellow. This is because pigments use subtractive color mixing, while light uses additive color mixing. With pigments, each color subtracted reflects less of the visible spectrum. With light, each color added contributes more wavelengths to the mix.
Additive vs. Subtractive Color Mixing
| Additive (Light) | Subtractive (Pigment) |
|---|---|
| Starts with darkness | Starts with white light |
| Adds wavelengths | Subtracts wavelengths |
| Primary colors are red, green, blue | Primary colors are cyan, magenta, yellow |
| Mixing primaries makes white | Mixing primaries makes black |
With additive color mixing, you start with darkness and add light wavelengths together to form colors. The more wavelengths you add, the closer you get to white light. With subtractive mixing, you start with white light and absorb certain wavelengths. The more wavelengths absorbed, the closer you get to black.
This difference in starting points accounts for the different primary color sets. Red, green, and blue are chosen for additive mixing because those are the primary wavelengths that make up visible white light. Cyan, magenta, and yellow are chosen for subtractive mixing because they each absorb one of the red, green, or blue primaries, respectively.
The Visible Spectrum of Light
The visible light spectrum that humans can see consists of wavelengths between about 380-750 nanometers. The longest wavelengths around 700nm appear red. The shortest wavelengths around 420nm look violet. Green wavelengths of light are around 520-565nm. Blue ranges from about 450-500nm.
When you look at a rainbow, you are seeing the visible spectrum spread out, with red on one end and violet on the other. A rainbow displays the full range of colors that make up white light when its wavelengths are separated.
| Color | Wavelength (nm) |
|---|---|
| Red | 700 |
| Orange | 620 |
| Yellow | 580 |
| Green | 520-565 |
| Blue | 450-500 |
| Violet | 420 |
When wavelengths of light mix together in the eye, the different cones and rods in our retinas allow us to perceive them as different colors. Red, green, and blue are the primary colors because those wavelengths align with the peak sensitivities of the three types of color-sensitive cones in the human eye.
Mixing Red, Green, and Blue Light
When beams of pure red, green, and blue light mix together, they produce the secondary colors of light:
– Red + Green = Yellow
– Red + Blue = Magenta
– Green + Blue = Cyan
Mixing all three primary colors of light together equally produces white light. This is because white light contains roughly equal parts of the visible spectrum.
The more dominant a primary color is in the mix, the closer the resulting color will be to that primary. For example, a mix with mostly red and a little green will appear orange. A mix with a lot of green and a little blue makes a bluish-green color.
Varying the proportions of the primaries creates all the colors humans can perceive. Computer screens and TVs take advantage of this by using many small red, green, and blue pixels to make the different hues in their displays.
Shades and Tints
Once you have mixed a color, you can create lighter or darker shades of it by adjusting the brightness or intensity. Adding white to a color makes it lighter, creating a tint. Mixing in black makes the color darker, making a shade.
For example, a pure vivid red can be lightened by adding white to make pink. Adding black will darken the red into maroon or burgundy. These variations in brightness while holding the hue constant are important for the many subtle gradations of color we see.
Color Perception and the Brain
Our experience of color involves much more than just the wavelength mix entering the eye. Complex neural processing occurs in the visual cortex of the brain to create our perceptions from sensory signals. Context, surrounding colors, and learned associations all affect how we see color.
For example, our brains automatically compensate for changes in lighting conditions. A white sheet of paper will still appear white to us whether we view it indoors under warm artificial light or outdoors on an overcast day. This color constancy allows us to perceive consistent colors despite differences in illumination.
Our perceptions can also be influenced by adjacent colors through simultaneous contrast. Placing a gray square on a green background will make it appear reddish. The same gray on a red background will look greenish. The contrast effect helps sharpen our perception of edges and boundaries.
Cultural Associations
Color meanings and symbolism are not fixed – they vary greatly between cultures, religions, and time periods. These associations are learned, not innate. For example, in many Western cultures, black is associated with grief and white with purity. But in some Asian cultures, white is the color of grief and mourning.
Meanings can also evolve within a culture over time. Pink was considered a masculine color in the early 1900s, while blue was seen as delicate and feminine. The current gender associations with blue for boys and pink for girls only solidified after World War II. Colors convey cultural concepts, not universal absolutes.
Practical Applications
Understanding how red, green, and blue mix together has many practical applications in digital image processing. Color adjustment tools like levels and curves rely on manipulating the RGB components to enhance images. Knowledge of primary colors guides white balance correction to remove unrealistic color casts from photos.
In printing and design, cyan, magenta, yellow, and black inks are combined using the CMYK color model to reproduce a wide gamut of hues. RGB and CMYK models have a complex relationship, connected by the underlying principles of additive and subtractive mixing. Mastering color theory leads to more accurate color representations.
Conclusion
When red, green, and blue light mix together in different proportions, they produce all the diverse hues we see in nature. Additive color mixing underlies the colors on all our digital screens. It also governs the interaction of light waves to form the visible spectrum. While physics determines the wavelengths of light, our human perception imparts the psychological experience of color. Understanding the basics of mixing primary colors gives insight into the interplay between the objective and subjective aspects of color.
