We all are aware that the rainbow consists of seven colors: Violet, Indigo, Blue, Green, Yellow, Orange & Red. The acronym VIBGYOR is a great way to learn all the colors that are included in rainbow. But if you remember, we were taught that there are three primary colors red, blue and yellow. Further these three combine to make three secondary colors known as orange, purple & green & other colors from different shades of three colors. So, basically there are six colors. Now a question arises from does this violet & Indigo come into the rainbow and who made that decision. The answer is once again Isaac Newton.
The Visual Spectrum
When it comes to color theory, then it is not as easy to understand as it seems. We usually mix different colors to get a new color based on a subtractive method, which basically combines the three primary colors like red, blue & yellow. But we see colors in light waves, & light combines colors according to the additive mixing method, which also uses the primary colors red, blue & green.
In the 17th century, Sir Isaac Newton is the one who realized that while breaking the white light apart using a prism or even rain drops, we get the visual spectrum of colored light. In the above image you can see, in the visual spectrum, each color has a shade of its neighbors. So, it is not a set of colors but a spectrum. But Newton decided we should probably break this spectrum up into different chunks so we have easy choices & talk about the colors.
Ancient Greece & the Magic of Seven
Let us trace the roots back to the 6th Century BC & also talk about a person generally known as Pythagoras. We all know the Pythagoras was a number fanatic as also used to apply numbers in the real world phenomena. He discovered that musical notes which are seven in number could be translated into mathematical equations, & he even had a theory which tells how the Seven heavenly bodies move according to the mathematician patterns. So, if you follow from the starting then Pythagoras showed that 7 was a magical or a special number that somehow disparate with natural phenomena. He further proves it as the sum of the spiritual(3) & the material(4).
In this time, Pythagoras also started a school where his ideas grew into philosophy called Pythagoreanism, mostly based on mathematics and mysticism. It was one of the reasons Pythagoreanism is great as it influenced some of the most popular thinkers including Plato & Aristotle. And that is one of the reasons why we have seven days in a week, seven deadly sins, seven dwarves, seven wonders of the world but how did it get applied to the rainbow?
The Circular Route from Pythagoras to Newton
One of the Pythagorean philosophers Philoalaus is still the first known person ever to live who posted that Earth revolves around a “central five” rather than everything revolving around the earth. This theory was used by another renowned person Copernicus who is now widely credited for developing heliocentric theory of planetary motion. And Newton also relied on this theory when creating his theory of gravity.
So, when he started to think about color, he subdivided the spectrum into five colors red, blue, yellow, green & purple but later revised this number to seven while adding orange and indigo as Pythagoras used to believe that there was a connection between color & music. As there are seven natural notes, so there has to be seven principal colors. So, this is the most known reason why the rainbow has seven colors.