The simple answer is yes, red, blue, and green are the primary colors and they can be combined to create any other color. This is due to the way our eyes perceive color through cells called cones that detect different wavelengths of light. By mixing different levels of the primary colors, we can trick our eyes into seeing millions of distinct hues. Let’s take a deeper look at how this works.
How the Eye Perceives Color
Human eyes have three types of cones that are each sensitive to different wavelengths of light. There are cones that detect long wavelengths (red light), medium wavelengths (green light), and short wavelengths (blue light). When light hits the eye, the cones send signals to the brain based on how much they are stimulated. The brain interprets these signals as color.
For example, when we look at an orange object, it is reflecting light with wavelengths in the red and green range. The red and green cones send strong signals while the blue cones send a weaker signal. The brain combines these into what we perceive as orange.
By mixing different levels of stimulation of the three cone types, all the colors we see can be created. This is known as the trichromatic theory of color vision. Essentially, any color can be matched by some combination of red, green, and blue light.
The RGB Color Model
The way screens like computer monitors and televisions produce color takes advantage of the trichromatic theory. Pixels on screens emit a combination of red, green, and blue light. By making each pixel produce different amounts of these primary colors, all colors can be simulated.
The levels of red, green, and blue light are each measured on a scale from 0 to 255. A value of 0 means none of that color is emitted, while 255 is the maximum amount. Here is an example RGB value for an orange color:
| Red | 244 |
| Green | 133 |
| Blue | 0 |
By mixing 244 units of red, 133 units of green, and no blue, the orange color is produced. All the colors we see on screens are combinations of red, green, and blue light emitted by pixels.
Combining Color Pigments
Unlike emitted light, pigments like paint and ink work by absorbing and reflecting different wavelengths. The primary colors of pigmentation are cyan (blue), magenta (reddish purple), and yellow.
When all three primary pigments are combined, they absorb most visible light wavelengths, resulting in black. With no pigment, most light is reflected and we see white. By mixing the primaries in different ratios, a wide gamut of colors can be created.
For example, red paint pigment absorbs cyan and reflects magenta and yellow light. Yellow absorbs blue and reflects red and green. When these two are mixed, both cyan and blue light are absorbed, leaving red and green to be reflected from the surface as orange.
The following table shows some common secondary colors created by mixing the primary pigments:
| Cyan + Magenta | Blue |
| Cyan + Yellow | Green |
| Magenta + Yellow | Red |
With various combinations and ratios, the primary pigments can create any color within the visible spectrum.
Light vs. Pigment Primaries
An interesting difference arises when comparing the primary colors of light and pigment. Red, green, and blue are the primaries for light while cyan, magenta, and yellow are the primaries for pigment. This seems contradictory at first.
The reason is because pigments work by selective absorption, while light works by additive emission. For absorbing pigments, magenta absorbs green, yellow absorbs blue, and cyan absorbs red, leaving other wavelengths to reflect. For emitting light, the primaries are red, green, and blue.
So while they seem inverted, the same principles of color mixing apply. By controlling the levels of the primary colors, any hue can be created with light or pigment.
Other Color Systems
While RGB and CMY are the most common methods of color mixing, there are other color models as well. Some examples include:
- RYB (red, yellow, blue) – Historical artists’ pigment primaries
- HSV (hue, saturation, value) – Commonly used in image editing software
- CIELAB – Models human perception of color difference
- Pantone – proprietary spot color matching system
These other color systems have their uses, but ultimately they depend on mixing varying levels of red, green and blue light or cyan, magenta, and yellow pigment to create all colors.
The Visible Spectrum
What we call visible light is electromagnetic radiation with wavelengths from about 380 to 700 nanometers that the human eye can detect. The longest wavelengths we see as red grading to shorter wavelength oranges, yellows, greens, blues, and finally violets at the shortest wavelengths. This span makes up all the possible colors our eyes can perceive.
But visible light is just a small slice of the full electromagnetic spectrum, which ranges from radio waves to gamma rays. Just outside the visible range is infrared starting at 700 nm and ultraviolet ending at 380 nm. Other animals can see colors in these ranges we cannot.
Within the visible spectrum, individual colors correspond to specific wavelength ranges. Here is a breakdown of the approximate wavelengths for common color names:
| Color | Wavelength range (nm) |
| Red | 620-750 |
| Orange | 590-620 |
| Yellow | 570-590 |
| Green | 495-570 |
| Blue | 450-495 |
| Violet | 380-450 |
So when we talk about red, green and blue as primary colors, we are referring to particular wavelength ranges of visible light. By mixing light from across this spectrum, any perceivable color can be created.
Cone Response Curves
Perceiving color depends not just on light wavelength, but how strongly the three cone types respond to given wavelengths. Each type of cone has a response curve showing how sensitive they are across different wavelengths.
Here is a diagram of the approximate cone response curves. Long wavelengths stimulate the red cones the most, medium wavelengths the green cones, and short wavelengths stimulate the blue cones.
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By stimulating the different cone types to varying degrees, all visible color sensations can be evoked.
Cone Density in the Eye
The three types of cones are not distributed equally across the retina. There are significantly more red and green cones than blue. Some estimates of cone density include:
- 64% red cones
- 32% green cones
- 2% blue cones
This imbalance means we perceive finer gradations in reds and greens than in blues. It is part of the reason blue screens are used as greenscreen backdrops for visual effects. The blue color is more strongly perceived against different brightnesses.
There is also spatial variation in cone distributions. The central fovea region has a higher density of cones while rods dominate in the peripheral areas. This results in our sharpest color vision being in the center of our view.
Cone Monochromacy
In rare cases, people can lack functioning cones of one or more types, resulting in color blindness. The specific condition depends on which cones are missing or non-functional:
- Monochromacy – Only one cone type works, so can only see shades of one color
- Dichromacy – One cone type does not work, usually red or green cones
- Anomalous Trichromacy – All cones work but one type has shifted sensitivity, causing color confusion.
Those with monochromacy and only blue cone response have the rarest form of color blindness. Without red and green cones, they can only see different shades of blue and yellow.
These individuals provide yet more evidence that mixing three primary colors is essential for normal human color vision. With only one or two cone types, a full color palette cannot be perceived.
Opponent Process Theory
An additional wrinkle in our perception of color is that the signals from cones appear to be processed in opponent pairs. Some examples of theorized opponent pairs include:
- Red vs. Cyan green
- Blue vs. Yellow
- White vs. Black
Rather than individual signals from each cone, it seems our brain compares ratios between cone responses in these opposing pairs. This adds additional processing of signals before color is perceived.
A result of this theory is that we do not perceive colors strongly in opponents together. We do not see strong blues with yellows or reds with greens. Environments trigger more red or green, blue or yellow in a scene.
The mechanisms behind opponent processing are complex and still not fully understood. But it further demonstrates that mixing three primary colors alone does not explain all aspects of color vision.
Tetrachromacy
If the trichromatic theory seems restrictive for capturing the variety of color, some humans potentially perceive even more. There is a rare condition called tetrachromacy where individuals have four different cone types. Some estimates suggest 1 in 100 people, mostly women, may possess tetrachromatic powers.
A fourth cone type beyond red, green and blue cones could allow someone to perceive colors invisible to the rest of us. However, most tetrachromats may not have full awareness and control over this ability without training.
But the existence of tetrachromacy suggests that even with three primary colors generating millions of hues, the human visual system may have room for even greater nuance in our perception of color.
Conclusion
By mixing three primary colors of light – red, green and blue – any color within the visible spectrum can be created. Pigments work similarly by absorbing other wavelengths when cyan, magenta and yellow are combined in different ratios. This trichromatic theory of human color vision accounts for the millions of distinct colors we can perceive.
Our remarkable ability depends on cone cells in the eye that are stimulated to varying degrees by light of different wavelengths. Responses from red, green and blue sensitive cones are processed by the brain to form our inner sensation of color.
So while they seem simple on the surface, combining primary colors allows for vast and nuanced visual experiences. Red, blue, and green truly make an entire world of color possible.