This story was created for the Google Expeditions project by Vida Systems, now available on Google Arts & Culture.
In order to talk about the science of color, a specific set of terminology is needed.
What Is Color?
To see color, 3 things are required – visible light, light receptors located in the eye, and the visual cortex located in the brain. If any of the last 2 are missing, this can result in visual impairment, or even blindness.
The Electromagnetic Spectrum
Light is part of the electromagnetic spectrum. The human eye is only able to detect a very small fraction of these wavelengths. This is called the visible light spectrum.
The Visible Spectrum
All of the visible wavelengths the human eye can detect are found within sunlight. Sunlight also contains energy traveling on wavelengths that the human eye cannot detect, namely infrared and ultraviolet light.
Colors of the Rainbows
When light is directed into a prism, white light becomes separated into the colors humans can see – red, orange, yellow, green, blue, indigo, and violet. Rainbows are created the same way when white sunlight is dispersed through water drops in the sky.
Objects do not contain a color themselves. Instead, the color perceived is due to the object absorbing some color wavelengths and reflecting others. For example, the first sphere is red because the sphere has absorbed all the other wavelengths but reflects red back.
Color in Nature
Nature has evolved to take advantage of the heat absorption/reflection that occurs through the absorption of colors. Many desert animals, like the Scimitar Oryx has white fur which has evolved to reflect heat away from the body.
It may seem that polar bears don't fit this idea. However, polar bears’ fur is actually clear and their skin is black in color, which will absorb heat from sunlight.
How Humans See Color
The human eye is designed to see color using photoreceptor cells called cones. Cones need light in order to work well, preferably normal or bright light. When all the cones work together properly, they sense the combinations of light waves so that we can see millions of colors!
Light from the Sun
All of the visible wavelengths the human eye can detect are found within sunlight. Sunlight also contains energy traveling on wavelengths the human eye cannot detect, namely infrared and ultraviolet light.
When light hits an object, some wavelengths are absorbed and turned into heat and other wavelengths are reflected. The reflected wavelengths are what we perceive as color.
The reflected wavelengths reach our eye by going through the pupil. They then travel past the lens and hit an area at the back of the eye called the retina.
The retina contains the photoreceptor cells which are designed to detect light, darkness, and some color wavelengths. There are actually over 120 million photoreceptor cells in each of your retinas!
Rods and Cones
There are 2 types of photoreceptor cells in the human eye. Rods detect light and dark while cones react to color wavelengths. Humans have 3 types of cones with each one sensitive to one color — either red, green, or blue.
The Optic Nerve
The red cones are activated by the red wavelength reflecting off the apple. These cones transmit this information from the retina in the eye to the brain via the optic nerve.
The wavelength information is delivered to the visual cortex. The brain uses this information, as well as other information the eye sends such as the origin of the light source, to perceive what color the object is.
How Other Species See Color
All color perceived by humans is a combination of 3 colors detected by photoreceptor cones located in the retina, inside of the eye. Since other species have different sets of photoreceptors, they therefore see the world and its colors very differently.
The retina located inside of the human eye contains 3 type of cones; red, blue, and green. Due to this type of eye structure, we can also be called trichromats.
Dogs only have 2 cones: blue and yellow. Therefore they cannot see red and green objects. So a red ball in green grass will be almost impossible for a dog to see.
The anatomy of snakes’ eyes vary widely among different species, mainly dependent on whether the snake is diurnal (hunts during the day) or nocturnal. Many snakes have an extra set of photoreceptors located near the nose which can detect heat.
Butterflies have 5 sets of cones, including colors humans are familiar with: red, green, and blue. Humans are unable to process what the other 2 cones detect. In addition butterflies can also see ultraviolet light which helps them in their search for pollen.
Mantis Shrimp Vision
Mantis shrimp are said to have the greatest eyesight of any known animal. They have 16 different photoreceptors, including red, blue, and green. Humans are unable to process what the other 13 cones detect.
They also see ultraviolet light, polarised light, and circular polarised light.
Why Do Humans and Other Animals See Color?
Currently there are 2 scientific theories which attempt to explain why the human race evolved to see colors only on the red, green, blue spectrum. Other species in the animal kingdom evolved to see different colors, depending on that species’ individual needs.
Colors of Food
For many years scientists believed humans evolved color vision in order to spot colorful fruit. However many other primates that also rely on fruit as a food source do not see the same colors as humans causing scientists to reconsider this theory.
Human’s Sensitivity to Red
New scientific theory suggests that the ability to see red in particular may also be important in recognizing sickness in other humans, as well as helping with communication. Sick humans can look flushed and blushing can indicate excitement, embarrassment, or fear.
Dogs’ vision evolved to detect movements from a great distance away. Dogs also possess sensitive photoreceptors which help them hunt during times of very low light, like dawn and dusk.
Butterflies can see ultraviolet light, which helps them find pollen-rich flowers. Some flowers in turn have evolved to have ultraviolet “pollen guides,” bright patches of pollen that reflect ultraviolet light and attract pollinators like butterflies.
A viper’s heat pits, holes located on its face, are special organs. These pits evolved to help the snake detect infrared and therefore see the body heat of its prey.
An eagle has 5 photoreceptor cone cells and can also see ultraviolet light. The ultraviolet light evolved to help the eagle find food by following the urine trails of small prey.
Humans are able to distinguish about 10 million different colors. How do you think this is possible when the human eye only contains 3 type of cones? The answer lies in color mixing. Here are examples of additive mixing and subtractive mixing.
Additive Color Mixing
Additive color mixing is used to make the colors displayed on computer screens. Additive color mixing begins with a black background and uses the colors red, blue, and green. When all colors are combined, white light is produced, giving a full color image.
Subtractive color mixing
Subtractive color mixing is used in printing, as the beginning background is white. Subtractive color mixing uses the colors yellow, magenta, and cyan. When all colors are combined, black is created.
Within any given subject or field, there are a specific set of terms used to describe processes or objects. People who use color extensively such as graphic designers, artists, printers, and painters have their own set of terminology to describe color.
Hue is the term used for color. There are 12 colors on the color mixing wheel: 3 primary colors, 3 secondary colors, and 6 tertiary colors. By mixing them, virtually infinite numbers of hues can be created.
Each of the 12 colors can be changed using one of 3 processes: tinting, shading, or toning. Tinting occurs when white is added to any of the 12 colors. For example, white can be added to red to make pink.
Shading occurs when the color black is added to any of the 12 colors on the color wheel. For example, black can be added to orange to create the hue brown.
A tone is created by adding gray (both black and white) to one of the 12 colors on the color wheel. It’s common for artists to mix a little gray into their paints to adjust the intensity of their pigment colors.