Why Isn't Yellow Considered a Fundamental Color in the RGB Model?

The RGB color model, a fundamental part of digital design and display, does not consider yellow as a primary or fundamental color. This is because the RGB model is based on the additive color theory, which uses red, green, and blue as the primary colors. Let's explore why yellow is not considered a fundamental color in the RGB model.

Additive Color Mixing

In the RGB system, colors are created by adding light. When red and green light are combined, they produce yellow. Thus, yellow is a secondary color in this model rather than a primary one. This is a key reason why yellow is not considered fundamental in the RGB model.

Different Color Models

Color models serve different purposes based on their applications. The RGB model is widely used in digital screens and lighting, while the CMY (cyan, magenta, yellow) and CMYK (cyan, magenta, yellow, black) models are used in printing. In the CMY model, yellow is a primary color. The disparity in the prioritization of certain colors across these color models elucidates why yellow is not fundamental in the RGB model.

Perception of Color

The way humans perceive color is based on the response of cone cells in our eyes. The RGB model aligns with how these cells react to different wavelengths of light, making red, green, and blue the fundamental components for creating a broad range of colors in light. This further reinforces the rationale for the RGB model's choice of primary colors, excluding yellow.

Trichromatic Vision and Animal Differences

Humans have trichromatic vision, which means we have three types of color receptors in our eyes. When we see an equal combination of red and green light, we perceive it as yellow. Adding more red light shifts our perception to orange, while adding more green light results in a perception of chartreuse.

Some animals have more diverse color receptor types. For instance, animals with RGBY (red, green, blue, yellow) receptors would perceive red and green differently, not as yellow. This difference in perception underscores the reasons why yellow is not a primary color in the RGB model.

Printing Color Models

For printing, a different color model is used, the CMYK (cyan, magenta, yellow, black) model. The inks in printers are cyan, magenta, and yellow, with a true black pigment added for a more accurate shade of black. Mixing the first three colors gives an unsatisfactory dark grey, hence the need for a separate black ink.

Light Refraction Through a Prism

When light passes through a prism, the main colors that emerge are red, green, and blue. This is why there is no yellow in the primary set of colors visible through a prism. The primary colors in a prism are often referred to as the visible spectrum, which includes red, green, and blue along with other colors.

In conclusion, while yellow is a significant secondary color in digital screens and lighting, its role as a primary color is not recognized in the RGB model due to its additive color theory and the way human vision perceives color. Understanding these concepts is crucial for anyone working with digital design and display technologies.