Last updated: January 21, 2026
[Original Japanese Version] This article is translation of the Summary of "Primary Color Principles", the #1 ranked resource on this topic in Japan. 光の三原色と色の三原色の仕組み（日本語版）
Summary
What are The Primary Colors of Light and Pigment？
Defining RGB and CMY
The Three Primary Colors of Light (RGB) are Red, Green, and Blue. By blending these three light sources in various proportions, a vast spectrum of colors can be created. When all three are combined at full intensity, they result in White light—a process known as Additive Color Mixing.
On the other hand, the Three Primary Colors of Pigment (CMY) are Cyan, Magenta, and Yellow. These are the fundamental colors for color material(colorant), such as ink and paint. By mixing these substances, they subtract light to create different colors, and combining all three results in a color approaching Black (Subtractive Color Mixing).
The Principles of Primary Colors of Light and Pigment
What are the Three Primary Colors of Light (RGB)?
The Three Primary Colors of Light consist of Red (R), Green (G), and Blue (B). These are the fundamental colors used in Additive Color Mixing, a process where colors are created by blending light sources.
When these three colors are mixed at equal intensity, they produce White light. This principle is widely applied in devices that emit light to reproduce colors, such as televisions, smartphones, and projectors.
In digital environments, the standard hex color codes for these primary colors are as follows:
Red (R): #FF0000 Green (G): #00FF00 Blue (B): #0000FF
The Principles of Primary Colors of Light
What are the Three Primary Colors of Pigment (CMY)?
The Three Primary Colors of Pigment consist of Cyan (C), Magenta (M), and Yellow (Y). These are the fundamental colors used in Subtractive Color Mixing, where colors are created by mixing colorants such as paints and inks.
In this process, each pigment absorbs (subtracts) certain wavelengths of light. When these three colors are mixed at equal intensity, they combine to produce Black. This principle is essential for reproducing colors in color photography, commercial printing, and inkjet printers.
In digital design environments, the standard hex color codes for these primary colors are as follows:
Cyan (C): #00FFFF Magenta (M): #FF00FF Yellow (Y): #FFFF00
The Principles of Primary Colors of Pigment
Comparison of the Primary Colors of Light(RGB) and Pigment(CMY)
| Item | Primary Colors of Light (RGB) | Primary Colors of Pigment (CMY) |
|---|---|---|
| Primary Colors | Red, Green, Blue | Cyan, Magenta, Yellow |
| Mixing Method | Additive Color Mixing (Becomes brighter as mixed) |
Subtractive Color Mixing (Becomes darker as mixed) |
| Full Mixture | White | Black |
| Main Uses | TVs, Smartphones, PC monitors, Lighting, etc. | Printed matter, Paints, Dyes, Inkjet printers, etc. |
| Mechanism | Produces color by emitting light directly. | Produces color by absorbing and reflecting light. |
The primary colors of light and pigment are deeply intertwined with the biological mechanisms of human color vision. In this article, we will explore the fundamental principles of color science, addressing the essential question—"Why are there only three primary colors?"—while providing an easy-to-understand explanation of the differences between additive and subtractive color mixing.
Furthermore, we will cover practical applications ranging from everyday technologies like smartphone and TV displays and printing techniques to cutting-edge innovations. By the end of this post, you will gain a systematic understanding of the fascinating phenomena of light and color.
RGB Color Mixing Simulator
In additive color mixing, adding more colors results in white.
CMY Color Mixing Simulator
In substractive color mixing, adding more colors results in black.
Human Color Vision
It is often explained that light is an electromagnetic wave and its color is determined by its wavelength. While this is not incorrect, color is not a universal property inherent in light itself; rather, it is something we perceive through our sense of vision. The fact that we can create a vast array of colors using only three primary colors is deeply rooted in the mechanism of human color perception.
The human retina contains two types of photoreceptor cells: rod cells and cone cells. Rod cells are highly sensitive to low light but cannot distinguish colors. In contrast, cone cells require brighter light to function and are responsible for our ability to perceive color. Cone cells are primarily concentrated in the fovea (the central part of the macula), while rod cells are more numerous than cone cells and are widely distributed throughout the peripheral areas of the retina. Through these two types of photoreceptors, the eye captures the brightness, color, and shape of objects imaged on the retina.
Structure of the eye and photoreceptor cells
The photosensitive substance found in rod cells is called rhodopsin, while the substance in cone cells is known as iodopsin. Both consist of a structure where a protein called opsin is bonded with retinal, a derivative of Vitamin A. While the structure of opsin differs between rod and cone cells, in both cases, the retinal exists in a cis-configuration when not exposed to light. Upon absorbing light, the structure of the specific part (indicated in red) changes, transforming into a trans-configuration.
Chemical Structures of Photopigments: Rhodopsin and Iodopsin
When the structure of retinal changes, the bond between the retinal and the opsin is broken. The reason rhodopsin's structure changes upon exposure to light is that visible light alters the electronic energy states of the molecule. This light-induced structural change in rhodopsin acts as the stimulus for the photoreceptor cells. This stimulus is transmitted through the optic nerve to the brain, resulting in the perception of sight.
The trans-retinal, once disconnected from the opsin, eventually reverts back to the cis-retinal form in the dark and recombines with the opsin. Additionally, retinal is synthesized from Vitamin A obtained through our diet. A deficiency in Vitamin A leads to difficulty seeing in low light (a condition known as night blindness) because the synthesis of rhodopsin becomes impaired.
Why Three? The Connection Between Primary Colors and Human Vision
There are three distinct types of opsins found in cone cells. Consequently, based on these differences in opsins, there are three types of cone cells: L-cones (Red cones), M-cones (Green cones), and S-cones (Blue cones), which are stimulated by red, green, and blue light, respectively. Each type is sensitive to a range of wavelengths centered around approximately 560 nm, 530 nm, and 430 nm. It should be noted that the "wavelength" referred to here is the wavelength of light in a vacuum or in the atmosphere. A difference in wavelength implies a difference in the light's frequency—that is, a difference in the energy of the light. Thus, the three types of cone cells are actually stimulated in response to differences in the energy of light, rather than the wavelengths themselves.
Spectral Sensitivity Curves of Cone and Rod Cells
The intensity of stimulation for the three types of cone cells varies depending on the light entering the eye. The signals from each cone cell are transmitted to the brain via the optic nerve. The brain then perceives specific colors based on the ratio of stimulation received from these three types of cones.
For example:
- When L-cones (red) and M-cones (green) are stimulated equally, the brain perceives yellow.
- When L-cones (red) and S-cones (blue) are stimulated equally, it perceives magenta.
- When M-cones (green) and S-cones (blue) are stimulated equally, it perceives cyan.
- When all three types of cone cells are stimulated equally, the brain recognizes the light as white.
Mammals were once nocturnal creatures, meaning they prioritized the ability to see in the dark over the ability to distinguish colors. As a result, many mammals, such as dogs and cats, possess dichromatic vision (two-primary color vision). In contrast, certain primates—including some prosimians, New World monkeys, Old World monkeys, apes, and humans—became diurnal, living in the bright light of day. This lifestyle shift led to the development of advanced color discrimination, resulting in trichromatic vision (three-primary color vision). The concepts of the three primary colors of light and pigment are derived from this trichromatic vision. The following figure shows the solar spectrum. It can be argued that human trichromatic vision evolved to efficiently utilize light in the 400 to 800 nm range, where solar radiation reaching the Earth's surface through the atmosphere is most abundant. Light within the wavelength range of 380 to 780 nm is referred to as visible light.
Solar Spectral Irradiance.png
The colors we perceive are, in fact, constructs of our brain, created based on the information from light entering our eyes. In reality, neither light nor objects possess inherent color. It is the brain that "paints" color onto the world. Light and objects merely provide the conditions that our color vision interprets. Color is nothing more than a concept we have created. It arises from the interplay between the components of light and our physiological visual system; it is not an intrinsic property of light itself. Animals with different types of color vision see a world of colors entirely different from our own. In this sense, the vibrant, multi-colored landscapes we see are a "virtual world" generated within our brains.
The Mechanism of Vision: Perceiving Shape and Color
Light entering the eye stimulates photoreceptor cells at the back of the retina. These stimuli are converted into electrical signals that travel through the optic nerve to the brain, allowing us to perceive the shapes and colors of objects.
Frequently Asked Questions (FAQ)
Q1: What is the biggest difference between the Primary Colors of Light and Pigment?
A: The main difference is how brightness changes when colors are mixed. The Three Primary Colors of Light (RGB) are based on Additive Color Mixing, where colors become brighter and closer to white as they are combined. In contrast, the Three Primary Colors of Pigment (CMY) are based on Subtractive Color Mixing, where pigments absorb light and become darker, approaching black as they are mixed.
Q2: Why is it fixed at "three" primary colors? Wouldn't four or five work?
A: This is because the human retina contains three types of sensors called "Cone Cells" (L, M, and S cones) that respond primarily to red, green, and blue wavelengths. Since our brain determines every color by processing the ratio of these three stimuli, a three-color combination is the most efficient and natural way to reproduce colors for human vision.
Q3: I learned in elementary school that the primary colors were "Red, Blue, and Yellow." Was that wrong?
A: It’s not wrong; rather, it is based on traditional art education (the RYB model). However, in modern optics and printing technology, the scientifically accurate primary colors that can reproduce the widest and most vivid range of colors are Cyan (blue-green), Magenta (red-purple), and Yellow.
Q4: Is there a trick to easily remembering "Complementary Colors"?
A: A great tip is to remember that RGB and CMY have a direct complementary relationship. Think of them in pairs: Red (R) vs. Cyan (C), Green (G) vs. Magenta (M), and Blue (B) vs. Yellow (Y). Remembering these pairs makes it much easier to understand the opposing relationships on the color wheel.
Q5: Why do printers use a separate "Black (K)" ink?
A: In theory, mixing Cyan, Magenta, and Yellow should produce black. However, because real-world inks contain impurities, mixing them usually results in a muddy dark brown instead of a true black. Therefore, a dedicated Black (K) ink is used to ensure sharp text and stable shadow tones in printing. The "K" stands for "Key plate," referring to the color that serves as the foundation for sharp outlines and text. Using a dedicated black ink ensures that dark elements are rendered clearly. In addtion, using black ink significantly saves on the consumption of CMY inks, as it eliminates the need to mix them to create black or gray tones.
Q6: What other mechanisms cause color to appear?
A: Beyond the mixing of primary colors discussed here, color can be generated by various physical properties of light. Examples include refraction (rainbows and prisms), thermal radiation (the color of stars), structural color caused by diffraction and interference (soap bubbles and the back of CDs), and metallic reflection caused by free electrons (metallic luster).
Author: Photon (Master of Engineering) Specialization: Optics, Optical Analysis, and Instrumental Analysis Publications: Author of several books on "Light and Color" and "Lenses" Member of The Japan Society for Analytical Chemistry (JSAC)
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