Color Vision: How Many Colors Can You Really See?

Close your eyes and think about the last sunset you saw. The deep oranges bleeding into pink, the violet edges of clouds, that impossible shade of gold right at the horizon. Now consider this: the person standing next to you may have seen an entirely different sunset, not because they were looking at something else, but because their eyes and brain process color differently than yours. Color vision is one of the most remarkable feats of human perception, and it varies far more from person to person than most people realize. In this article, we will explore how color vision works, why some people see more (or fewer) colors than others, and how to test your own color perception.

How Human Color Vision Works

Trichromatic Vision

Human color vision is based on three types of cone cells in the retina, each sensitive to different wavelengths of light. This is called trichromatic vision. The three cone types are:

• S-cones (short wavelength): Peak sensitivity around 420 nm, perceiving what we call blue-violet light
• M-cones (medium wavelength): Peak sensitivity around 530 nm, perceiving green light
• L-cones (long wavelength): Peak sensitivity around 560 nm, perceiving red-yellow light

Your brain does not directly perceive wavelengths. Instead, it compares the signals from all three cone types and constructs a color experience based on the ratios. For example, when your L-cones fire strongly and your S-cones fire weakly, your brain interprets this as “red.” When both L-cones and M-cones fire equally with minimal S-cone activity, you see “yellow.” This opponent-process comparison is how we perceive the full spectrum of colors from roughly 380 nm (violet) to 700 nm (red).

A typical human with normal trichromatic vision can distinguish approximately 1 million different colors. This is possible because the brain can detect subtle differences in the ratios of cone signals.

Rod Cells and Scotopic Vision

In addition to cones, the retina contains approximately 120 million rod cells. Rods are extremely sensitive to light but do not discriminate color. They are responsible for vision in low-light conditions (scotopic vision). This is why colors appear to wash out in dim lighting and you see primarily in shades of gray at night.

Tetrachromacy: Seeing Beyond Normal

One of the most intriguing discoveries in color science is tetrachromacy: the possibility of having four types of cone cells instead of three. Tetrachromacy has been confirmed in many species (birds, fish, reptiles), and there is growing evidence that a small percentage of humans, almost exclusively women, may be functional tetrachromats.

The genetic basis is as follows: the genes for M-cones and L-cones are located on the X chromosome. Women, having two X chromosomes, can potentially carry variant cone genes on each chromosome, resulting in four distinct cone types. Research by Dr. Gabriele Jordan at Newcastle University identified women who could consistently distinguish colors that looked identical to normal trichromats.

Estimates suggest that 2-3% of women may have the genetic potential for tetrachromacy, but functional tetrachromacy (actually using the fourth cone type to perceive additional colors) is extremely rare. A functional tetrachromat could theoretically distinguish up to 100 million colors, one hundred times more than a typical trichromat.

Color Blindness: Types and Prevalence

On the other end of the spectrum (literally), color vision deficiency (commonly called color blindness) affects a significant portion of the population. It occurs when one or more cone types are absent or function differently than normal.

Red-Green Color Blindness

This is by far the most common type, affecting approximately 8% of men and 0.5% of women of Northern European descent. It comes in several forms:

• Deuteranomaly (reduced M-cone sensitivity): The most common form, affecting ~5% of men. Greens appear more red/brown.
• Protanomaly (reduced L-cone sensitivity): Affects ~1% of men. Reds appear more green/brown and are less bright.
• Deuteranopia (missing M-cones): Affects ~1% of men. Cannot distinguish red from green at all.
• Protanopia (missing L-cones): Affects ~1% of men. Similar to deuteranopia but with dimmer reds.

Blue-Yellow Color Blindness

Tritanomaly (reduced S-cone sensitivity) and tritanopia (missing S-cones) are much rarer, affecting less than 0.01% of the population. Unlike red-green deficiencies, these affect men and women equally because the S-cone gene is on chromosome 7, not the X chromosome. People with blue-yellow deficiency have difficulty distinguishing blue from green and yellow from violet.

Complete Color Blindness (Achromatopsia)

True color blindness, where a person sees only in shades of gray, is extremely rare. Rod monochromacy (complete achromatopsia) affects roughly 1 in 30,000 people. These individuals have no functioning cone cells and rely entirely on rods. They experience not only a complete absence of color but also extreme light sensitivity and reduced visual acuity, since rods provide much lower resolution than cones.

The Ishihara Color Test Explained

The most widely used color vision screening test is the Ishihara test, developed by Japanese ophthalmologist Dr. Shinobu Ishihara in 1917. The test consists of circular plates filled with colored dots of varying sizes. Within each plate, a number or pattern is visible to people with normal color vision but hidden to those with specific color deficiencies.

The standard Ishihara test includes 38 plates, though shorter versions (14 or 24 plates) are commonly used for screening. The plates fall into several categories:

• Demonstration plates: Visible to everyone, used to confirm the person understands the test
• Transformation plates: People with normal vision see one number, while those with a deficiency see a different number
• Vanishing plates: The number is visible only to people with normal color vision
• Hidden digit plates: The number is visible only to people with a color deficiency
• Diagnostic plates: Help distinguish between protan and deutan deficiencies

While the Ishihara test is excellent for detecting red-green deficiencies, it does not test for blue-yellow deficiency or measure the severity of color vision loss. More comprehensive tests like the Farnsworth-Munsell 100 Hue Test can provide detailed assessment of color discrimination ability across the entire spectrum.

How Color Perception Varies Day to Day

Even with normal color vision, your perception of color is not constant. Several factors cause it to fluctuate:

• Lighting conditions: Colors look different under fluorescent, incandescent, and natural light (this is called metamerism)
• Age: The lens of the eye yellows with age, reducing blue light transmission. People over 60 may perceive blues as more muted.
• Fatigue: Tired eyes have reduced color discrimination ability
• Screen calibration: Different monitors display colors differently. Online color tests are less reliable than clinical tests for this reason.
• Chromatic adaptation: After staring at one color for an extended period, your perception of other colors shifts temporarily

Test Your Color Vision

Curious about how well you see color? CalcViral's color vision test uses Ishihara-style plates and color arrangement challenges to assess your color discrimination ability. While online tests cannot replace a clinical examination, they can give you a solid indication of whether your color vision is normal, and if not, what type of deficiency you may have.

Take the test in a well-lit room, on a calibrated monitor if possible, and make sure your screen brightness is set to a comfortable level. Try it at different times of day to see how your performance varies.

Final Thoughts

Color vision is a deeply personal experience. What you call “blue” may look subtly different to the person next to you, and neither of you would ever know. From the 100-million-color world of potential tetrachromats to the grayscale reality of achromatopsia, the range of human color experience is staggeringly wide. Understanding your own color vision is not just a curiosity but it can inform career choices (pilots, electricians, and designers all need good color discrimination), help you understand why certain color combinations look “off” to you, and give you a deeper appreciation for the incredible neural processing happening behind your eyes every waking moment.