Colors make our world bright and cheerful. Colors are everywhere: green in leaves, blue in our sky, and brown in soil. Animals use colors to attract mates (peacocks) or warn away their predators (frogs). For us, a world without colors is unimaginable. But how do we see colors?
Table of Contents
The word “color” reminds us of a rainbow. How does a rainbow appear? A rainbow is an arc with layers of different colors: ROYGBIV – Red, Orange, Yellow, Blue, Indigo, Blue, Violet. However, scientists now claim that the rainbow is only made of six colors, as the human eye cannot differentiate between blue and indigo.
Can we see it on a sunny day? No. We only see a rainbow in the sky on a rainy day. Sunlight is white in color, and when it passes through raindrops it forms a rainbow by a process called refraction. Refraction is the bending of light as it passes from one medium (air) to another medium (water drops). Colorless, transparent light is a mixture of many colors.
Can we make an artificial rainbow? Yes, we can, when light such as sunlight or a flashlight’s beam passes from one media to another, such as from air to water or from air to a transparent glass such as a prism. Bingo! We have a rainbow in our living room, study, bedroom, or anywhere. A rainbow is formed when white light splits into six colors. So, the natural light that we see is actually a blend of six colors.
What is light?
On entering a dark room, we cannot see anything. What do we need? A light. Light is a form of energy that helps us to see things.
So, can we see all light? No, because light of different wavelengths exists. The human eye can only see the light of wavelengths between 380nm and 750nm, called the visible spectrum.
Can all living things see the same spectrum?
No. Each species has a different visual spectrum. As in the image, dogs and humans see different spectral wavelengths.
How do objects appear colorful?
Ever wondered why a red delicious apple looks red? This is because red light bounces off or reflects off the apple. But how? The light that falls on the ball is white; but we know that white light is made of different colors: VIBGYOR. So, your favorite fruit looks red because it has reflected red color and absorbed other colors.
When light falls on an object, some of the colors get “absorbed” by the object and other colors are “reflected.” The color reflected from the object reaches our eyes and we see the object and its color.
Now, what about white- and black-colored objects? A white object reflects all wavelengths, and a black object absorbs all wavelengths.
We now understand colors. So, let’s play some fun pop quiz. Look down and see if you can answer them
1. Red apple: reflected color is RED
2. White paper: reflected color is VIBGYOR
3. Yellow sunflower: reflected color is YELLOW
4. Black paper: reflected color is NO COLOR. All colors are absorbed. (Hint: it’s the opposite of white paper).
How does the eye detect color?
The retina is the most critical part of an eye for vision. It is the cell layer at the back wall of the eye which senses light and sends a signal to the brain.
The retina has specialized cells, called photoreceptor cells, which convert light into signals and transmit them to the brain. There are two types of photoreceptor cells: rods and cones.
Rods are photoreceptor cells sensitive to dim light. They help us to see in poor light.
There are about 120 million rods in the retina.
Cones are photoreceptor cells involved in seeing color. There are about 60 million cones localized in the center of our retina. Cones work in bright light, help us to see color, and give a sharp image. There are three types of cone cells corresponding to the primary colors: Red-sensing cones, Green-sensing cones, and Blue-sensing cones.
How do we see colorful objects?
A colored object will excite all three types of cones, but at varying degrees. For example, a green ball will stimulate the green cones to a large extent, but also the red cones to a lesser extent and blue cones to an even lesser extent. We perceive color based on the superposition of different spectra conveyed to the brain.
What are Primary, Secondary, and Tertiary colors?
- Primary colors are not produced by mixing other colors. They are red, blue, and yellow.
- Secondary colors are obtained by mixing equal parts of primary colors. They are green, orange, and purple. Green is a blend of blue and yellow, orange is a blend of red and yellow, and purple is a blend of red and blue.
- Tertiary colors are a blend of a primary and a secondary color.
What Is Color Blindness?
Color blindness is an inheritable disorder in which a person cannot distinguish between colors. Color blindness happens when one or more types of cone cells are absent or not functioning properly.
Most people have a mild color deficiency and can see colors normally in good light but have difficulty in dim light. Some people can see only some colors. In very rare instances, some people see everything in shades of grey.
Celebrities with color blindness:
John Dalton, Rod Stewart, Mark Zuckerberg
Conclusion
Color perception is a complex science that blends biology, chemistry, and physics.
References
1. Jacobs, G.H., & Nathans, J. (2009) Color Vision: How Our Eyes Reflect Primate Evolution. Scientific American. 300(4), 56–63.
2. https://askabiologist.asu.edu/rods-and-cones
3. https://www.britannica.com/science/color/The-visible-spectrum
Glossary
1. Electromagnetic radiation: a form of energy that includes radio waves, microwaves, X-rays, gamma rays, and visible light
2. Visible spectrum: an electromagnetic spectrum from 380nm–750 nm that is visible to the human eye
3. Rods: a type of photoreceptor cell in the retina which helps us to see in low light
4. Cones: a type of photoreceptor cell in the retina which helps us to see different colors
5. Wavelength: the distance between two successive crests or troughs in a wave. Light is a wave, and so has a wavelength.
