Maggie sent me a tweet this morning about purple. It claimed that purple was not real, but merely a mental construct. This inspired Paw and me to do a little research.

Purple is considered a mental construct because, in terms of light wavelengths, there is no specific wavelength of light that corresponds to "purple." The visible light spectrum ranges from red to violet, with each color having a distinct wavelength. Purple, however, does not exist as a single wavelength of light. Instead, our brains perceive purple when we see a combination of red and blue light, which are at opposite ends of the visible spectrum. Our brain blends these colors and creates the perception of purple, making it a construct of how we process and interpret color rather than an inherent property of light.

The reason our brains evolved to perceive purple likely has to do with the way human vision developed. Our eyes have three types of color receptors (cones) sensitive to red, green, and blue light. When both red and blue cones are stimulated simultaneously, the brain interprets this as purple. This capacity allows us to perceive a wider range of colors, helping us distinguish between objects and their surroundings in complex environments.

There are several colors that, like purple, do not correspond to a single wavelength of light but are instead mental constructs created by the brain. These colors are called non-spectral colors because they do not appear in the visible spectrum as a result of a single wavelength of light. Here are some of the main ones:

1. Purple

Why it's a construct: As mentioned earlier, purple is a combination of red and blue light. There is no wavelength for purple; it is perceived when both red and blue cones in the eye are stimulated simultaneously.

2. Pink

Why it's a construct: Pink is a mixture of red and white light. There's no pure wavelength of light that corresponds to pink—it results from light of various wavelengths being combined. Like purple, pink is something our brain constructs from different visual inputs.

3. Brown

Why it's a construct: Brown is not found in the visible spectrum as a single wavelength. It is a darkened version of orange or yellow, typically perceived when a combination of low-intensity red, orange, and yellow light is seen. Our brains interpret this blend of wavelengths as brown, particularly in the context of contrast with brighter surrounding colors.

4. Magenta

Why it's a construct: Magenta is similar to purple in that it arises when both red and blue light are combined, with no green light present. Like purple, there’s no single wavelength for magenta, and it exists purely as a product of the brain interpreting opposing ends of the spectrum together.

5. White

Why it's a construct: White light is not a single wavelength but rather a combination of all wavelengths of visible light. When our eyes receive light from across the spectrum in relatively equal amounts, our brains interpret it as white.

6. Gray

Why it's a construct: Gray, like white, is also a product of the combination of light from across the spectrum but at lower intensity. It doesn’t correspond to a single wavelength but instead results from light that is weak across all wavelengths, producing a desaturated, low-light version of white.

7. Black

Why it's a construct: Black is essentially the absence of light. It is not a color in the traditional sense but the perception of no light reaching the eye. Our brains perceive black when very little or no light is present, yet it is treated as a color by the mind.

8. Beige

Why it's a construct: Beige is a mixture of low-intensity light across a range of wavelengths, much like brown. It’s not a spectral color because no single wavelength corresponds to beige, but the brain constructs it when we see a soft combination of colors, usually involving light brown, yellow, or gray tones.

These non-spectral colors demonstrate that much of color perception is the result of the brain processing various wavelengths of light and combining them to create colors that don't physically exist as single wavelengths. Our brains are wired to fill in these gaps and allow us to perceive a full range of colors that enhance our visual experience.

Source: ChatGPT (2024, September 18).
Image: color-meanings.com