Cambridge Color Test

What is the Cambridge Colour Test?

The Cambridge Colour Test (CCT) is a computerized color vision test developed at the University of Cambridge by John Mollon and Polly Reffin and used in eye clinics and research worldwide. Instead of asking you to read numbers like the Ishihara plates, it shows a Landolt C — a ring with a gap — made of colored dots on a background of dots with random size and brightness. Because the brightness is random, the only way to find the C is by its color, so the test measures color vision on its own.

The best-known version, the Trivector test, measures how much color difference you need to see the C along three directions in color space: the protan, deutan and tritan confusion lines — the color changes that people with red-weak, green-weak and blue-weak vision respectively find hardest to see. The test adapts as you answer, so it reports a threshold for each axis rather than a simple pass or fail. This page is an online color vision test based on that method; it is not the official Cambridge Colour Test and is not affiliated with Cambridge Research Systems, which publishes the clinical version.

How this online Cambridge color test works

Every stimulus is drawn fresh in your browser: a field of dots, eight levels of brightness chosen at random for each dot, and a C whose dots are shifted in color by a precise amount along one confusion line in the CIE 1976 u′v′ color space. Three staircases run interleaved, one per axis: each correct answer makes the next C on that axis harder to see, and each mistake makes it easier. After the staircase has reversed direction several times, the average of the last reversals is your threshold.

Results use the same units as the clinical test — u′v′ × 10⁻⁴. In published data for adults with normal color vision, protan and deutan thresholds are typically below about 100 and tritan thresholds below about 150; tritan thresholds rise gradually with age. Red-green color deficiencies raise the protan and deutan thresholds, with the higher of the two pointing to the type, and dichromats often reach the largest difference the screen can show.

Cambridge color test vs. Ishihara-style plates

Plate tests such as our color blind test are quick screens: they tell you whether you can read a number designed to be invisible to a particular deficiency. A color discrimination test like this one goes further — it measures how much color difference you need on each axis, which makes it better at grading mild deficiencies (anomalous trichromacy such as deuteranomaly), at picking up blue-yellow (tritan) loss that many plate tests miss, and at tracking changes over time. The trade-off is that it takes longer and is more sensitive to screen settings.

If you want to see what these deficiencies actually look like, open any image or color in the color blindness simulator. Designers can use the results to choose palettes that stay distinct for everyone — check pairs in the contrast checker and build schemes with the palette generator.

Getting an accurate result online

The clinical Cambridge Colour Test runs on a calibrated display in a darkened room. At home, a few things make a big difference: turn the brightness up, switch off every color filter (Night Shift on Mac and iPhone, Night Light on Windows, True Tone, f.lux, reading modes), avoid strong colored room light, and use a reasonably good laptop or desktop monitor rather than a phone in sunlight. Viewing angle matters on cheaper screens, so sit straight in front of it.

Because no two screens show color identically, compare your thresholds with each other more than with the published numbers: a tritan threshold far above your protan and deutan ones, or one red-green axis much higher than the others, is the meaningful pattern. Retaking the test on the same screen is a good way to check a surprising result. For anything that matters — a job requirement, a sudden change in your color vision, or a medical question — see an optometrist or ophthalmologist.

Cambridge color test FAQ