Normalized typical human cone cell responses (S, M, and L types) to monochromatic spectral stimuli
The color purple in a rainbow
In a rainbow the colors order is red then orange (made from red and yellow, thus making sense that it appears in between them) the yellow followed by green after which comes blue (again green formed from yellow and blue). The final color is purple, which is next to the blue’ but not in any contact with the red. The question is – is there any actual connection between the colors and there source as known to as (such as orange from yellow and red, the last two being the source) to its appearance in a rainbow? If so, why doesn’t the purple follow the same logic? How is the purple seen were it is seen in a rainbow (where there is no red nearby)?
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asked Mar 24, 2013 at 18:05
user22362 user22362
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$begingroup$ Tip: Before asking a new question, it is a good idea to search the Phys.SE site to see if an answer to your question already exists. $endgroup$
Mar 24, 2013 at 18:14
$begingroup$ This question may provide some insight to you: scicomp.stackexchange.com/q/5554 $endgroup$
Mar 24, 2013 at 18:22
$begingroup$ No, you’re wrong. There are not 3 colors and others made from them. Orange is not formed from red and yellow in the rainbow. Sunligh is a continuum spectrum. There are actually all wavelenghts, including all oranges and midtons, without mixture. And, wether purple is there or not has been already discussed here. $endgroup$
Oct 7, 2018 at 17:39
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It does follow the same logic. There are some barely seen mini rainbows in the outer layers called supernumeraries. The red on the supernumerary overlaps some of the blue on the original.
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answered Nov 21, 2014 at 17:25
Adam Adam
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There exists an extensive article in wikipedia where color is analyzed both from the physics aspect and the biological aspect.
In short there exists the physics spectrum of light with a one to one correspondence to frequency, and color as perceived by the eye, which has three types of cone cells for light perception, and builds up color recognition from this.
Normalized typical human cone cell responses (S, M, and L types) to monochromatic spectral stimuli
So even though the light spectrum has a color response identified with a frequency, our perception of color allows us to see colors that do not correspond to that spectrum frequency. An interesting effect is the polaroid colored pictures that used red green and blue pigments to generate colored pictures.
The Color Purple — In Physics
You may have heard of the book The Color Purple by Alice Walker, but what does the mixture between red and blue mean for your eyes?
Purple has been used by millions of individuals, ranging from Roman magistrates and high-priced Phoenician purple dye. It was first introduced in the Neolithic era, in which it was used by French Pech Merle artists, and later the Tyrian people in the 15th century BC. It was later passed to China through the purple gromwell plant, then the Byzantine Empire, and then was propagated throughout the Renaissance period and to centuries beyond, finally making its way into our century through years of use, interpretation, and association, and made its way to becoming the 11th most popular color in America, and was named the color of the year for two years in a row by Pantone. It is now seen in dyes, clothing, plants, lightning, graphic design, user interfaces, product packaging and more.
The color purple is associated with thousands of things: the book, wealth, royalty, extravagance, magic, pride, independence, the mattress company, regality, and grandeur, among other descriptive adjectives, but it takes on a whole new meaning from a physics standpoint.
Purple is commonly known as the color produced when red and blue are mixed. This is true, but not holistically. Purple, not to be confused with violet, is actually a large range of colors represented by the different hues created when red, blue, or violet light mix. Purple is a color mixture, whereas violet is a spectral color, meaning it consists of a single wavelength of light. In fact, purple doesn’t have its own explicit wavelength, making it unique in observation. Due to this, purple is not the principle color of magenta, crimson, or indigo, either, though they are perceptually very similar to one another. On the CIE Chromaticity Diagram (the image above), there is a given purple boundary, which is a line of purples located between spectral red and violet colors that are seen on the graph. But then here lies an important question:
Why do I see purple instead of violet or indigo or even magenta?
The answer is simple: it is purple. Just kidding. It’s not that simple. In fact, you’re not seeing purple at all, according to our current physics. Purple as a color doesn’t necessarily even exist, kind of like magenta, due to it not having a static wavelength. So even though we only see red, green, and blue, when we look at any color on the same spectrum of blue, pink, and violet, there is a large range of wavelengths that reach our eyes during the same concurrent moment as we’re looking at an object. Due to the conic nature of our retina, we process an extremely large amalgamation of light reflections, the ratio of which is to be seen as a perfect spectral color. So, in reality, you are seeing violet; red and blue with a little more blue, whereas when you see purple, it’s more of a red and blue 1:1 situation. In reality, purple, being a perfect fraction of a color, resembles so many other colors, and because it is so mundane, our brains have recognized other colors to be shades of it, even spectral and primary ones!
So what does this all mean?
Well, I hate to disappoint you, but this means virtually nothing in your daily life. Perhaps you’ll be more considerate to violet or magenta when you see them, but I don’t think it will cause you to win the lottery or ace your exam (article on that coming soon). However, if you’re looking to work with spectroscopy, optical physics, or even with using samples in genetics or programming materials, understanding light interactions, visual perception, and photoluminescence will be quite important. Anyway, if you see violet around make sure to not say: “Hey! You look like purple!”
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Various cultures view purple as the color of royalty.
Many cultures and religions revered purple, largely because of its scarcity. In China, purple dye was made out of purple gromwell, a plant native to eastern Asia. The dye didn’t always stick to fabric, so using it for clothing was extremely expensive. The Byzantine Empire believed purple to be a gift from God. The oldest surviving text of the New Testament, the Codex purpureus Rossanensis, is on purple pages with gold and silver lettering. The births of emperors born into power took place in purple rooms to distinguish them from those who only rose to power by war.
The Romans weren’t the only ones to ban non-royalty from wearing the coveted color. In 1547, Henry Howard, the Earl of Surrey, was charged and executed for committing treason against Henry VIII after, in part, being seen wearing the color of the king. Henry VIII’s daughter Elizabeth I also refused to let anyone but royalty wear the color.
Technically, purple doesn’t exist.
There are seven colors within the visible spectrum of light: red, orange, yellow, green, blue, indigo, and violet. Each color has its own corresponding wavelength and frequencies. When these waves overlap, they create a new color. Sir Isaac Newton made this discovery in the 1600s, when he discovered that white light is a mix of all seven colors bouncing back and being perceived by the receptors in the eyes.
Purple is a mix of the red and blue waves overlapping as they bounce back. Purple (and all it shades) are the colors our brain interprets when looking at red and blue together. While some people may point out that violet is a spectral color, violet is not purple. Although they’re often used interchangeably and look extremely similar to each other to the naked eye, they’re different. For one, violet surpasses blue on the visible spectrum and has the shortest wavelength. Furthermore, as Minute Physics explains, what we call violet should actually be considered blue, and what we call blue should be considered cyan.
Carrots used to be purple.
When we think of carrots, we think of the bright orange vegetable that Bugs Bunny eats while asking “what’s up, doc?” Today, carrots are mainly orange, but this wasn’t always the case. The earliest record of carrot cultivation comes from 10th-century Persia. These veggies were purple and white with thin roots.
While there may have been orange carrots then, they were a rare mutation. It’s believed that in the 16th century, Dutch growers started developing orange carrots using the mutated strains to produce a sweeter vegetable. While purple carrots still exist today, they aren’t as common as their orange counterparts.
