Most humans see about 1 million colors. A small percentage of women may see 100 million — because they have a fourth type of color receptor that the rest of us lack.
Normal human vision is trichromatic — three types of cone cells (red, green, blue) combine their signals to produce every color you've ever seen. But roughly 12% of women carry a gene for a fourth cone type, sensitive to wavelengths between red and green. In rare cases, this fourth cone is functional — and the world splits into a kaleidoscope the rest of us can't imagine.
Each additional cone type doesn't just add colors — it multiplies them. A trichromat distinguishes ~100 shades per channel (100³ = 1 million combinations). A fourth channel yields 100⁴ = 100 million. The math is exponential, not additive.
Note: this test runs on a standard RGB monitor, which can only display trichromatic color. A true tetrachromacy test requires controlled spectral light — this is just a discrimination sensitivity check.
The genes for the red and green cone pigments sit on the X chromosome. Women have two X chromosomes, so they can carry two slightly different versions of the same cone gene — one on each X. If the two versions differ enough, the brain treats them as separate channels. Men, with only one X, can only have one version of each.
This is also why color blindness is almost exclusively male (8% of men vs 0.5% of women). The same genetic mechanism that protects women from color blindness also gives some of them a shot at super-vision. The mothers and daughters of colorblind men are the most likely tetrachromat candidates.
"I've always seen more colors than other people could name. I thought everyone could see the shimmer in shadows, the warmth in grays. They couldn't." — Concetta Antico, confirmed tetrachromat and artist
Australian artist Concetta Antico is one of very few confirmed functional tetrachromats. Under spectral testing at UC Irvine, she demonstrated the ability to distinguish colors that look identical to trichromats. Her paintings are famously vivid — not because she exaggerates, but because she's painting what she literally sees.
The challenge for researchers: having the fourth cone is necessary but not sufficient. The brain must also wire itself to use the extra signal, which may require a lifetime of exposure during critical visual development periods. Many women carry the gene. Very few are functional tetrachromats.