Indigo is one of the colors in the visible spectrum that makes up the rainbow. The rainbow is composed of seven distinct colors – red, orange, yellow, green, blue, indigo, and violet. These colors range from longer wavelengths of light to shorter wavelengths, with red having the longest wavelength and violet having the shortest. So where does indigo fall in this spectrum of colors? Here’s a quick overview of the color indigo and its place in the rainbow.
Defining Indigo
Indigo is a deep blue color that lies between blue and violet on the visible spectrum. It has a shorter wavelength than blue and a longer wavelength than violet. The word indigo comes from the Greek word indikon, meaning “blue dye from India.” This refers to the blue dyestuff that was originally extracted from the indigo plant and used to color fabrics.
Some key facts about the color indigo:
| Wavelength range | About 450–420 nanometers |
| Hex triplet | #4B0082 |
| RGB values | R: 75 G: 0 B: 130 |
So indigo has a wavelength between 450-420 nm, putting it next to violet at the short wavelength end of the visible spectrum. It is much darker and deeper than the pure spectral blue color.
Indigo in the Rainbow
When white light from the sun passes through a prism, it separates into the visible spectrum of colors ranging from red to violet. Indigo appears as one of the seven main bands of color in a rainbow between blue and violet:
| Red | Orange | Yellow | Green | Blue | Indigo | Violet |
Indigo is the sixth color of the rainbow, occupying a small band sandwiched between blue and violet. It is difficult to distinguish indigo as a separate color in rainbows because the bands blend smoothly into one another. Most people perceive only six distinct color bands in the rainbow rather than seven.
Some key facts about indigo’s place in the rainbow:
| Wavelength range | 450-425 nm |
| Adjacent colors | Blue and violet |
| Hard to distinguish | Indigo band is very narrow |
So while indigo has its own wavelength range within the visible spectrum, it is not always easy to pick out as a distinct band of color in the rainbow.
How We See Indigo
The human eye contains photoreceptor cells called cones that allow us to perceive different wavelengths of light as distinct colors. There are three types of cones:
| Cone type | Color detected |
| S or Blue cones | Shorter blue wavelengths |
| M or Green cones | Medium green wavelengths |
| L or Red cones | Longer red wavelengths |
Indigo stimulation is detected mainly by the blue cones but also partially by red and green cones. This combination allows the brain to interpret indigo as a distinct bluish-purplish color different from blue and violet. However, because indigo occupies a very narrow band of the spectrum, we have difficulty distinguishing it as a separate color in the rainbow.
Historical Significance of Indigo
The seven colors of the rainbow including indigo originated in ancient Greece. However, the philosopher Isaac Newton was the first to scientifically demonstrate that white light splits into a visible spectrum when passed through a prism. He identified seven main colors, keeping indigo distinct from blue and violet.
Later scientists found that the number of color bands depends on how broad the bands are defined to be. When divided more narrowly, indigo could be considered part of the blue or violet bands rather than its own distinct color. But Newton’s seven rainbow colors including indigo remained convention.
Some key historical facts about indigo:
| Origin | Ancient Greece |
| Confirmed by Newton | In 1704 |
| Number of bands arbitrary | Depends how divided |
So while indigo may not occupy a very wide range of wavelengths, it holds historical significance as one of the seven original colors of the rainbow defined by Newton.
Distinguishing Indigo
To distinguish indigo from surrounding blue and violet in the rainbow, here are some tips:
– Look for the color between blue and violet. Indigo is the next band closer to violet than blue.
– Try to see seven distinct color bands instead of just six. Indigo will occupy the slim band right before violet.
– Note the deep purplish-blue tone compared to true blue. Indigo is much darker than blue.
– Compare indigo to violet. Violet is more reddish-purple than indigo.
– Use a prism to split sunlight and see the indigo band yourself.
– Use an image editing program to isolate the indigo band of a rainbow photo.
– Match the indigo band to Pantone or Crayola indigo crayon colors.
So while it takes a discerning eye to pick out indigo, looking for its darker tone compared to blue and more purplish tone compared to violet can help distinguish it.
Other Interesting Facts About Indigo
Beyond its place in the rainbow, here are some other interesting facts about the color indigo:
– Isaac Newton originally called indigo “indigo blue” since he saw it as a type of blue.
– The indigo plant has been used for centuries to create blue textile dyes around the world.
– Indigo dyes were very important economically during the 18th and 19th centuries.
– Denim fabric is dyed with indigo, originally using natural plant dyes.
– The deep blue color of blue jeans comes from the indigo dye used historically.
– Indigo has spiritual meaning in many cultures and is associated with the “third eye” chakra.
– The color electric indigo, a bright tone, was invented in the 1980s using only synthetic pigments.
So while one of its key uses is as a natural blue dye, indigo also has cultural significance as a color connected to spirituality, intuition, and the mystical. It continues to have modern applications in textile dyeing, digital arts, and more.
Conclusion
In summary, indigo occupies the slim band between blue and violet at the short wavelength end of the visible color spectrum. While it can be hard to distinguish as a separate color, indigo has historical origins as one of the seven colors of the rainbow as defined by Newton. With its deep bluish-purple tones, indigo carries cultural meaning and has long been used as a natural dye for textiles like denim. So next time you view a rainbow, see if you can spot the indigo band as a bridge between blue and violet in the sky.
