The colors of the rainbow have fascinated people for centuries. We typically think of the rainbow as having 7 colors – red, orange, yellow, green, blue, indigo, and violet. But some argue that there are actually more than 7 colors in a rainbow. So how many colors are there really in a rainbow? Let’s take a closer look.
The traditional 7 colors
The 7 color rainbow is the most common way to classify the spectrum of light that appears in the sky when sunlight interacts with moisture in the atmosphere. This pattern was first proposed by Isaac Newton in the late 17th century. Newton identified the main rainbow colors as red, orange, yellow, green, blue, indigo, and violet – hence the popular “ROY G BIV” mnemonic.
This 7 color sequence has become the standard model for rainbows in science and culture. Each color represents a specific wavelength of visible light:
| Color | Wavelength (nm) |
|---|---|
| Red | 620-750 |
| Orange | 590-620 |
| Yellow | 570-590 |
| Green | 495-570 |
| Blue | 450-495 |
| Indigo | 440-450 |
| Violet | 380-440 |
So in terms of the visible spectrum of light, there are 7 clear color bands that comprise a rainbow. This is why most representations of rainbows show these 7 archetypal colors.
The debate over 13 colors
While 7 colors is the standard, some argue that there are actually 13 distinct colors in a rainbow when you look closely. Proponents of the 13 color model claim that the traditional 7 bands don’t capture subtle hues between the main colors.
So what are the 13 rainbow colors? Building on the 7 color sequence, the extra 6 colors are:
- Red
- Orange
- Yellow
- Chartreuse green
- Green
- Blue-green
- Blue
- Violet
- Purple
- Rose
- Magenta
- Vermilion
- Scarlet
Chartreuse green, blue-green, rose, vermilion and scarlet are added as intermediate colors between the main 7 bands. Magenta is also included between violet and red to complete the cycle.
Proponents of the 13 color model argue that it more accurately reflects the full spectrum of hues that can be observed in a rainbow under ideal conditions. The distinction comes down to how finely the rainbow color spectrum is divided up.
Science behind rainbow color perception
So which perspective on rainbow colors is more scientifically sound? Let’s look at what optics and perception science tells us.
First, rainbows are optical phenomena caused by light refraction and dispersion through water droplets. Sunlight entering a raindrop is refracted and split into its spectral components, causing the rainbow pattern when leaving the droplet. Different wavelengths of light are refracted at slightly different angles, creating the color spectrum.
In theory, there is a continuous spectrum of infinite wavelengths and hues in a rainbow. But the human eye and brain can only perceive a finite number of distinct colors based on the peak sensitivities of the light-detecting cone cells in our retinas. There are three types of cones that are most sensitive to long (red), medium (green) and short (blue) wavelengths.
So we can’t actually see millions of distinct colors in a rainbow due to biological constraints. Our color vision system groups similar wavelengths into discrete perceptual categories for efficient processing. This is why the rainbow appears as color bands.
That said, some people may be able to perceive subtle color differences within the main 7 rainbow bands. Color discrimination varies between individuals based on factors like sex and age. Females tend to have better color perception on average than males. So the ability to see 13 or more colors in a rainbow comes down to individual color vision abilities.
Number of colors people can distinguish
Studies testing human color discrimination shed light on how many colors people are able to practically tell apart. Research suggests that the average person can perceive between 10 and 20 million distinct colors under ideal lighting conditions. But the actual number we can cleanly categorize and name is much lower.
Various studies have tested how many basic color terms people consistently use to classify color samples. Results indicate that the average person uses between 5-15 basic color categories like red, green, blue and so on. There is also cultural variation, as some languages have more or fewer color names.
So based on perceptual research, it seems reasonable for someone with good color acuity to distinguish between 10-15 principal colors in the continuous rainbow spectrum. The 13 color model falls within this range.
Best way to observe a rainbow’s colors
To maximize potential rainbow colors, here are some viewing tips:
- Look at brighter primary rainbows rather than secondary or double rainbows, which are dimmer.
- Block the sun partially with your hand or a building to reduce glare and boost color saturation.
- Look near the top or bottom of the arc so sunlight passes through more atmosphere.
- Perceive colors using central vision, as peripheral vision sees fewer hues.
With ideal conditions, some may see up to 13-15 rainbow colors. But the commonly cited 7 colors remain a reliable model for the main bands most people observe.
Conclusion
While the traditional 7 colors adequately describe a rainbow’s basic color sequence, an argument can be made for up to 13 discernible colors under optimal viewing conditions. The ability to distinguish more subtle hues comes down to individual variations in color vision. But the difference between 7 and 13 colors is ultimately just where we categorically divide up the seamless rainbow spectrum, rather than a fundamental physical property of rainbows themselves.
