Color is a fundamental part of human perception and experience. We see color all around us, from the green trees and blue skies, to the diverse hues of human skin, hair, and eyes. Color helps us identify and distinguish objects, and evokes psychological and emotional responses. But where do colors come from? How is the vast spectrum of color created from light?
The Origins of Color
At the most basic level, color originates from light. Sunlight appears white to our eyes, but it is actually composed of a spectrum of different wavelengths of light. When sunlight passes through a prism, the different wavelengths are refracted at different angles, splitting the white light into the colors of the rainbow.
The visible spectrum of light that humans can see ranges from violet light with short wavelengths, to red light with longer wavelengths. The wavelengths in between make up the other colors – blue, green, yellow, orange. So in that sense, all color originates from different wavelengths along the spectrum of visible light.
The Visible Spectrum
| Color | Wavelength (nm) |
|---|---|
| Violet | 380-450 |
| Blue | 450-495 |
| Green | 495-570 |
| Yellow | 570-590 |
| Orange | 590-620 |
| Red | 620-750 |
This table shows the visible spectrum of light that humans can see, ranging from violet with the shortest wavelengths, to red with the longest wavelengths. The wavelengths in between correspond to the other colors of the rainbow.
The RGB Color Model
While the visible spectrum shows that all color originates from different wavelengths of light, the specific colors that we perceive are actually created by a combination of three primary colors of light: red, green, and blue.
This is known as the RGB or red, green, blue color model. The RGB model is used for color reproduction – for example in television screens, computer monitors, cameras, and other imaging devices.
These devices use tiny dots or pixels of phosphors that emit colored light when excited by electrons. By combining different intensities of red, green, and blue light, any color can be reproduced. Mixing red and green makes yellow, red and blue makes magenta, and green and blue makes cyan. All three together in full intensity appears white.
Varying the intensity levels of the RGB components allows for the display of millions of colors. For example:
| Color | Red Value | Green Value | Blue Value |
|---|---|---|---|
| Red | 255 | 0 | 0 |
| Green | 0 | 255 | 0 |
| Blue | 0 | 0 | 255 |
| Yellow | 255 | 255 | 0 |
This table shows how colors are created by mixing different levels of the red, green, and blue components.
Trichromatic Theory
The idea that all colors can be matched using three primary colors is known as the trichromatic theory. This theory was first proposed by Thomas Young in the early 19th century. He hypothesized that the retina contained three types of color photoreceptor cells, which were preferentially sensitive to red, green and blue light.
Later work in the 1960s by physiologists confirmed the existence of these three types of cone cell photoreceptors. The peak sensitivities of the cone cells roughly correspond to red, green, and blue light. Signals from these three cone types are processed by the visual system to produce the perception of a wide range of colors.
The Human Eye
The trichromatic theory is the basis for how the human eye and visual system perceives color through the three types of cone cells. The retina contains about 120 million rod cells that detect brightness, and about 6 million cone cells that detect color.
There are three types of cone cells:
- S cones – Most sensitive to short wavelengths of light like blue and violet.
- M cones – Most sensitive to medium wavelengths like green.
- L cones – Most sensitive to longer red wavelengths.
Signals from these three cone types are processed in parallel nerve pathways that converge and mix in the visual cortex, allowing the perception of any color through varying stimulation of the cone cells. This trichromatic theory explains how the eye can detect millions of colors using only three receptor types.
Cone Cell Absorption Spectra
| Cone Type | Peak Sensitivity | Absorption Range |
|---|---|---|
| S Cones (Blue) | 420 nm | 400-500 nm |
| M Cones (Green) | 534 nm | 450-630 nm |
| L Cones (Red) | 564 nm | 500-700 nm |
This table shows the peak sensitivity and absorption range for the three cone cell types. The combination of signals from these three cones allows the eye to perceive the full range of visible colors.
Cone Cells and Color Deficiency
The trichromatic theory also helps explain color deficiencies like color blindness. This can occur if one or more of the cone cell types is absent or not functioning normally.
For example, in red-green color blindness, the L and M cones are affected, making it hard to distinguish red and green hues. In blue-yellow color blindness, the S cones are affected. Complete color blindness, where none of the cone types work correctly, is very rare.
So in summary, the three types of cone cells allow the human visual system to cover the full spectrum of visible light, providing trichromatic color vision. Defects in the cone cells lead to color vision deficiencies.
Additive and Subtractive Color Mixing
The RGB color model uses additive color mixing. This means the primary colors of light are added together to make other colors. Starting with darkness, adding more colors creates lighter and lighter hues.
In contrast, subtractive color mixing starts with white light and colors are created by subtracting wavelengths using pigments or filters. The CMYK color model uses subtractive mixing with the primary colors of cyan, magenta, and yellow. Combining these absorbs parts of the white light spectrum.
Computer screens and displays use additive RGB color mixing. Printed materials like books, magazines, and photographs use subtractive CMYK mixing. Both models rely on mixtures of three primary colors, and both can reproduce a wide range of hues.
Other Color Models
The RGB and CMYK models are the two most common ways of representing color, but there are other color models as well.
The HSV model represents hue, saturation, and value/brightness. HSL is similar representing hue, saturation, and lightness. These models separate out the chromatic/color content (hue and saturation) from the luminance or brightness.
There are also color models based on mixing pastels or paints. The RYB model uses red, yellow, and blue as primary colors. CMY is a simplified subtractive model for mixing pigments.
So while RGB and CMYK are the most widely used, other color models exist for different applications and with different advantages. But most still rely on three primary colors to recreate the variety of hues visible to the human eye.
The Uniqueness of Color
An interesting thing about color is that it is not an inherent property of light or objects themselves. Color is created in the brain and visual system. There is no color that exists outside of perception.
Wavelengths of light have no color on their own. They only produce color once processed and interpreted by the visual system and brain. In a sense, color is a creation of the mind.
This gives color a strangely elusive quality. The red of an apple and green of a leaf have no reality outside of our subjective experience of them. Yet color is also such a fundamental part of perception and interacts so deeply with mood, feelings, and aesthetics.
So in that sense, the experience of color is uniquely tied to biology and human consciousness. The wavelengths of the physical world take on color only through the lens of the mind and visual system.
Color and Wavelength Interactions
When multiple wavelengths of light mix, the results can be complex. Sometimes the wavelengths combine to form a new color sensation. Other times they can cancel out or interact in different ways.
For example, red and blue light shone on the same spot appears magenta. This is not awavelength found in the spectrum – it is a color created in the eye by combining the responses from the L and S cones.
Mixing green and red light creates yellow. This is an additive combination of the wavelengths. However, mixing green and red pigments creates a dark brown by subtracting parts of the spectrum.
Some pairs like green and magenta or blue and yellow are opposite colors and cancel each other out. These complex combinations show how color perception depends on both the physics of light as well as biological processing in the visual system.
Color Constancy and Perceptual Constancy
People tend to perceive color as relatively constant, even as lighting conditions change dramatically. This ability of the visual system is called color constancy.
For example, a white sheet of paper appears white to us in sunlight, shade, or under artificial lights. But the actual wavelength mix hitting the eye in each case is quite different. Still the brain compen
