When you mix the colors blue and red together, the resulting color is purple. This can be easily observed by mixing paints, dyes, or other pigments. But why does this specific combination of colors produce purple? The answer lies in the science of light and color.
The Basics of Light and Color
In order to understand why blue and red make purple, we first need to review some basic concepts about light and color.
Visible light is part of the electromagnetic spectrum. It travels in waves, with each color having a specific wavelength. The wavelengths of light determine what color our eyes perceive. Red has the longest wavelength, while violet has the shortest. The other colors of the rainbow – orange, yellow, green, blue, indigo – have wavelengths between these extremes.
When all wavelengths of visible light are combined together, the resulting color is white. Objects appear to have color because they absorb and reflect different wavelengths. For example, an object that appears red absorbs most wavelengths and reflects back the longer red wavelengths to our eyes. An object that appears blue absorbs most wavelengths except for the shorter blue wavelengths.
So in summary, color comes from different wavelengths of light, and the color we see depends on which wavelengths are reflected back to our eyes.
Mixing Color Pigments
When working with paints, dyes, or inks, the colors come from pigments. Each pigment absorbs and reflects different wavelengths of light. When two pigments are mixed together, the mixture reflects back a new combination of wavelengths, which our eyes and brain then interpret as a new color.
For example, red pigment absorbs most wavelengths of light and reflects back the longer red wavelengths. Blue pigment absorbs most wavelengths except the shorter blue ones. When red and blue pigments are combined, the resulting color reflects back both the long red wavelengths and the short blue wavelengths – and this combination is perceived as the color purple.
The following table summarizes the wavelengths absorbed and reflected by red, blue, and purple pigments:
| Color | Wavelengths Absorbed | Wavelengths Reflected |
|---|---|---|
| Red | Shorter wavelengths | Longer red wavelengths |
| Blue | Longer wavelengths | Shorter blue wavelengths |
| Purple (mixture) | Medium wavelengths | Short blue + long red wavelengths |
So when red and blue pigments are mixed, the new purple color reflects back both the red wavelengths and the blue wavelengths together.
Mixing Colored Light
The same principle applies when mixing colored lights. Red light is composed of long red wavelengths, while blue light contains short blue wavelengths. When red and blue light are combined, the result is light containing both red and blue wavelengths, which is perceived as purple.
Televisions and computer screens provide a good example of mixing colored lights to create different hues. These displays use tiny red, green, and blue light emitting diodes (LEDs) to create the colors we see. By varying the brightness of the red, green, and blue LEDs in different combinations, all the colors of the rainbow can be produced.
Mixing bright red light with bright blue light will produce bright purple light. Televisions mix red, green and blue light together in different proportions to display any color imaginable. So the same physics of combining wavelengths operates whether mixing pigments or mixing colored lights.
The Visible Spectrum
We can also see how red and blue make purple by looking at the visible light spectrum. As noted earlier, red light has the longest wavelengths while violet has the shortest. The colors fade gradually from red to violet in the sequence ROYGBIV (red, orange, yellow, green, blue, indigo, violet). Purple sits between blue and red in this sequence.
| Color | Wavelength (nm) |
|---|---|
| Red | 700 |
| Orange | 620 |
| Yellow | 580 |
| Green | 530 |
| Blue | 450 |
| Indigo | 445 |
| Violet | 400 |
So purple light is a mixture of the longer red wavelengths (around 700 nm) and the shorter blue wavelengths (around 450 nm). When our eyes see this combination of wavelengths together, we perceive the color purple.
Psychology of Color Perception
An interesting question is why we perceive purple or any other color at all from different wavelengths of light. In reality, wavelength mixes that produce colors like purple have no distinct boundaries. Red gradually fades into purple, and purple gradually fades into blue across the spectrum. So why do we see distinct bands of color rather than a smooth gradient?
The answer involves the biology of our eyes and neural processing in our brains. We have three types of cones cells in our eyes that are sensitive to different wavelength ranges. Signals from these cone cells are then processed by neurons in the visual cortex of our brains. This neural processing produces the distinct color perceptions that we experience.
So the perception of purple when red and blue are mixed is not an arbitrary choice. It results from the wavelengths of light triggering certain cone cells in our eyes and patterns of neural activity in the visual cortex. This allows the brain to distinguish different colors based on wavelength combinations.
History and Uses of the Color Purple
Now that we understand the science behind mixing blue and red to create purple, we can briefly explore the history and uses of this distinctive color.
Purple has long been associated with royalty, nobility, luxury, and ambition. This stems from the rarity and cost of the dye originally used to produce purple cloth. Purple dyes were extracted from a species of sea snail called Murex in ancient times. Thousands of snails were required to produce even a small amount of purple dye, making purple fabric extremely expensive. As a result, purple clothing was reserved for the emperor, nobles, and high officials in ancient Rome, Byzantium, and Persia.
The rarity and cost of Murex purple led it to be considered the color of royalty, status, and ambition. Emperors and kings were described as being “born to the purple”. The expression “purple prose” refers to pretentious and elaborate writing. Wealthy Roman citizens wore togas with purple borders as a display of status. The Christian church also adopted purple vestments and regalia for bishops as a symbol of authority and nobility.
Later on, cheaper purple dyes using lichens and other compounds were developed. This made purple clothing more accessible. Still, its association with status and ambition continued. Purple remains a popular color in fashion, interior design, art, flags, company logos and more.
Conclusion
So in summary, combining the colors blue and red produces the color purple in light and pigment. This occurs because blue light/pigment reflects short blue wavelengths, while red reflects longer red wavelengths. Together, a mix of blue and red produces reflected light containing both wavelengths, which is perceived as purple. The history of purple as a rare and expensive dye led to its association with royalty and status. But at the root, the purple hue arises from the intrinsic physics of red and blue wavelengths combining together.