Purple is an enchanting color that has captivated people for centuries. But is it a color that actually occurs in the natural world or is it simply a human creation? The answer is more complex than you might think.
What Is Purple?
Purple is what is known as a secondary color. This means it is created by combining two primary colors – blue and red. When these colors are mixed together on the visible spectrum, the resulting color is purple.
This is different from primary colors like red, yellow and blue which can be seen in the rainbow. Secondary colors only occur when primary colors are blended together.
So purple does not have its own dedicated wavelength of light. This means that true purple shades do not occur as a pure color in nature.
Where Does Natural Purple Come From?
While true purple is not found as a single wavelength of light, there are some natural ways that the color purple is formed in plants and animals.
Anthocyanins
One way purple occurs is through pigments called anthocyanins. These are water-soluble pigments that appear red, purple or blue depending on the pH level. They act as a type of natural pH indicator changing color based on the acidity levels.
Anthocyanins are very common in plants and fruits. When the pH levels are neutral, they appear more red or pink. But when in an alkaline environment with a higher pH, anthocyanins shift to a more purple or blue hue.
For example, anthocyanins are the reason purple asparagus turns green when cooked. The heat neutralizes the acidity causing the pigments to shift from purple to green.
Some common purple/blue foods and flowers that contain anthocyanins include:
- Blueberries
- Eggplants
- Purple cabbage
- Cherries
- Purple corn
- Grapes
- Violets
So while these plants are not naturally purple due to a specific light wavelength, they do contain natural pigments that cause them to reflect light in the purple spectrum.
Structural Color
In addition to pigments, some animals display purple and blue hues due to structural coloration. This refers to microscopic structures in feathers, scales, hair and skin that interfere with how light is reflected.
These structures cause specific wavelengths of light to be amplified more than others. In some birds and insects, this structural coloration results in vibrant blues, purples and greens.
Some examples of natural structural color include:
- Peacock feathers
- Butterfly wings
- Hummingbird feathers
- Mallard duck feathers
The most famous blue and purple structural colors occur in peacock tail feathers. The feathers have a complex microscopic structure that amplifies blues and greens while absorbing other colors.
As light hits the feathers, the nanostructures filter out red and yellow light waves, causing the remaining blue and green wavelengths to be reflected back more intensely. This makes the feathers appear blue and green from most angles. But as the viewing angle changes, the structures also reflect wavelengths of light that we see as purple.
Purple Minerals
There are also a small number of minerals that naturally form in purple shades. These geological formations occur when trace impurities or oxidation states cause the minerals to absorb and reflect light in the blue to red wavelengths.
Some examples of purple minerals include:
- Sugilite
- Charoite
- Purple halite
- Lepidolite
- Purpurite
- Cuprite
However, these purple minerals are relatively rare. The most common purple mineral, sugilite, was only discovered in 1944. So purple is an uncommon color in geological formations.
Purple Plants
In addition to fruits and vegetables that appear purple due to anthocyanins, some plants naturally grow in shades of purple due to genetics. These plants have purple leaves, stems, flowers or bracts (specialized leaves).
Some examples of genetic purple plants include:
- Purple heart plant
- Purple shamrock
- Purple fountain grass
- Purple coneflower
- Purple basil
- Purple sage
- Jacaranda tree
These plants inherit their purple color from naturally occurring variants in chlorophyll production that lean toward the red end of the light spectrum. This causes them to absorb more green/yellow light, leaving more blue/purple light to be reflected.
Purple Animals
There are also a number of animals that display true purple or violet coloration:
- Purple frog – This frog from India secretes a purple pigment possibly as an antibacterial or antifungal agent.
- Violet gobies – These small fish from the Caribbean have a deep bluish-purple coloring.
- Violet snail – This sea snail from the Pacific Ocean has a smooth purple shell.
- Violet birdwing butterfly – Endemic to Papua New Guinea, the males of this species have deep purple wings.
- Axolotls – These salamanders come in a variety of colors including purple and lavender.
Additionally, there are many species of octopus, nudibranchs (sea slugs), jellyfish and coral that naturally display stunning violet and purple tones.
Purple Bacteria
There are even a handful of purple bacteria species:
- Chromobacterium violaceum – A Gram-negative species of bacteria found in soil and water that produces purple pigment.
- Janthinobacterium lividum – A purple non-sulfur bacteria found in aquatic and soil environments.
- Rhodobacter capsulatus – These purple nonsulfur bacteria carry out photosynthesis.
- Rhodospirillum rubrum – Another purple photosynthetic bacteria species.
These bacteria derive their color from pigments like carotenoids and bacterioruberins that absorb and reflect light in the purple/red spectrum.
Purple Lighting Effects
There are also certain lighting effects in nature that can result in purple colors:
- Sunrises and sunsets – The scattering of sunlight through the atmosphere at sunrise or sunset removes greens and yellows leaving more reds and blues. This mixes to create vibrant violets, pinks and purples.
- Rainbows – Since purple sits between blue and red on the light spectrum, an especially vibrant rainbow with clear delineation between the colors will feature a band of purple.
- Lightning – Similar to a rainbow, branching lightning can separate wavelengths of light. This can result in fleeting purple light in a thunderstorm.
- Aurora borealis – The interaction of charged particles with atmospheric gases can cause streams of purple light in the northern lights.
Conclusion
So while true purple is not found as a pure spectral wavelength in nature, there are many examples of plants, animals, minerals, bacteria and natural phenomena that appear purple or violet due to pigments, structural color, genetics, lighting conditions and other factors.
Purple occupies an intriguing space between the primary colors of red and blue. So while elusive, purple can still emerge through the interplay of natural mechanisms across many species and settings. The fleeting, magical nature of purple may be what instills it with such allure.
Summary
Here are some of the key ways purple coloration occurs in nature:
| Origin of Natural Purple | Examples |
|---|---|
| Anthocyanin pigments | Blueberries, purple sweet potatoes, violets |
| Structural color | Peacock feathers, hummingbird feathers |
| Purple minerals | Sugilite, charoite, purpurite |
| Genetic plant variants | Purple basil, jacaranda |
| Purple animals | Purple frogs, violet snails, gobies |
| Purple bacteria | Chromobacterium violaceum |
| Lighting effects | Sunrises/sunsets, rainbows, lightning |
So in summary, while purple is a secondary color that does not exist as a single wavelength, nature has found diverse ways to produce fleeting flashes of this magical color through ingenious structural mechanisms across many living organisms and natural phenomena.
