There is an ongoing debate around whether purple is considered a color or a shade. At a basic level, purple is created by combining the primary colors red and blue. However, unlike other secondary colors like orange and green, purple does not have its own place on the visible color spectrum. This has led some to classify it as a shade rather than an independent color. In this article, we will analyze the scientific and historical evidence around purple to determine whether it qualifies as a color or a shade.
The Science of Purple
In physics, color is determined by the wavelength of visible light that an object reflects or emits. The visible spectrum ranges from violet with short wavelengths to red with longer wavelengths. Secondary colors like purple do not occupy a specific wavelength, but are combinations of two primary wavelengths.
| Color | Wavelength Range |
|---|---|
| Red | 620-750 nm |
| Orange | 590-620 nm |
| Yellow | 570-590 nm |
| Green | 495-570 nm |
| Blue | 450-495 nm |
| Violet | 380-450 nm |
As we can see, purple does not occupy a single wavelength on the visible spectrum. When we see purple, it is a mix of red light around 700 nm wavelength and blue light around 450 nm wavelength. This stimulates both the red and blue color receptors in our eyes and our brain interprets this combination as purple.
In contrast, orange occupies its own wavelength range of 590-620 nm. Light in this range stimulates the orange receptors in our eyes independently. So orange can be considered a distinct spectral color while purple cannot. This analysis suggests purple is not a true color but a combination of two primary colors.
How the Human Eye Perceives Color
Our perception of color is also linked to the biology of our visual system. Human eyes contain photoreceptor cells called cones that respond to different wavelengths of light. There are three types of cones:
– Short wavelength cones (S cones) detect blue/violet light
– Medium wavelength cones (M cones) detect green light
– Long wavelength cones (L cones) detect red light
When light hits our eyes, it stimulates these photoreceptors to varying degrees. Our brain combines the signals from the three cone types to give us our color perception. For example, L cones stimulate strongly when we see red colors while S cones respond more to blue shades. Purple triggers both S and L cones moderately but does not stimulate M cones.
Interestingly, some scholars believe that because purple does not strongly trigger any one type of cone, we perceived it differently than other colors like red and blue. We have to rely more on cognitive interpretation rather than direct sensory stimulation. This also supports the idea that purple is more of a constructed shade rather than an absolute color.
Purple in Nature
Another way to consider purple’s status is to look for examples of it in the natural world. In contrast to other colors, there are very few naturally occurring purple pigments or compounds.
Red, yellow, green and blue exist abundantly in minerals, plants and animals. Even violet, which is closest to purple on the spectrum, is found in many flowers like violets, orchids and lilacs. But true purple is quite rare. Some exceptions include:
– Purples and mauves found in sea slugs.
– Deep purple feathers in certain birds like pigeons.
– Some vineyards cultivate specific grapes to produce purple-red wines.
But overall, purple rarely occurs independently in nature. This scarcity again implies it may be a constructed blend of basic colors rather than its own spectral wavelength.
Purple in Human History
Looking at the historical use of purple also gives some clues to its status. In ancient times, purple was associated with extravagance and royalty because the dyes used to color fabric purple were extremely rare and expensive.
The Phoenicians gathered small mollusks that secreted a purple fluid to produce the Tyrian purple dye. It took thousands of mollusks and complex processing to create enough rich purple for a garment. As a result, only rulers could afford purple clothes and it became a symbol of high social status.
Later on, cheaper dyeing methods were invented using vegetable sources like madder and indigo. This made purple more widely available and expanded its use in art and fashion. But the regal history and lavish connotations contributed to purple being seen as unique and almost unnatural compared to common colors like red or green.
Modern Definitions
With the rise of modern color theory in the 18th and 19th centuries, definitions emerged to categorize purple:
| Classification | Definition |
|---|---|
| Primary color | A color that cannot be created by mixing other colors, in art usually red, blue, and yellow. |
| Secondary color | A color made by mixing two primary colors, e.g. purple, orange, green. |
| Spectral color | A color with specific wavelength on the visible spectrum. |
| Non-spectral color | A color not part of the visible spectrum, made by mixing spectral colors. |
| Shade | A darker version of a color, created by adding black. |
| Tint | A lighter version of a color, created by adding white. |
Under these definitions, purple is classified as a secondary non-spectral color, meaning it is made by combining two primary colors but does not have its own spectral wavelength. This separates it from pure spectral colors like red, blue, and yellow.
At the same time, purple does not fit the definition of a shade, as adding black to purple creates a different color like deep plum. And adding white makes lavender, rather than a lighter purple. So purple occupies a unique intermediary position between colors and shades.
Conclusion
Based on this analysis of the scientific, historical and definitional evidence, purple seems to exhibited characteristics of both a primary color and a shade:
– Purple does not have its own wavelength on the visible light spectrum, suggesting it is not a pure spectral color.
– The eye perceives purple through a combination of blue and red cones, not stimulation of a single cone type.
– Natural purple pigments are extremely rare compared to other colors.
– Purple was historically created through elaborate processes, not derived simply from a plant or mineral.
– Modern color theory defines purple as a secondary non-spectral color.
At the same time, purple does occupy its own unique place on the color wheel between red and blue and fulfills the general definition of a secondary color. Adding black or white to purple produces different shades and tints, not the original purple.
So in summary, purple exists in a fascinating gray area between color and shade. While not a pure spectral color, it still is defined as a distinct secondary color. Purple’s blend of two primary wavelengths gives it a singular identity not quite like any other color or shade. In both science and culture, purple occupies a liminal space that combines color and shade properties.
