Hue Sort Test

The Farnsworth-Munsell 100 Hue Test was published by Dean Farnsworth in 1943 and has been a standard of clinical colour vision testing ever since. It consists of caps of equal lightness and equal saturation whose hues step evenly around the colour circle, divided into four trays with a fixed reference cap at each end. The person taking the test arranges each tray into a smooth progression. Because the caps differ only in hue, and only slightly, the arrangement someone produces is a direct record of how finely they can separate one hue from its neighbour. Despite the name, there are 85 caps rather than 100.

This version keeps the method and rebuilds the caps for a screen. Instead of reproducing the physical pigments, the series here is defined in CIELAB, a colour space designed so that equal numerical distances correspond roughly to equal perceived differences. Every cap sits at the same lightness and the same chroma, and the 85 hues are spaced evenly around the full circle, which puts adjacent caps about 1.8 units apart — near the threshold at which most people can still tell two patches apart when they sit side by side. The caps are shown on a plain, uncoloured background, because a coloured surround shifts the appearance of everything placed on it.

Your result leads with how closely the order you built matches the order the caps actually run in. It is a rank correlation: every one of the 81 movable caps is compared with the position it belongs in, a cap one step out of place costs a little and a cap far from home costs a great deal, and the four fixed reference caps are excluded because they were never yours to move. A flawless sort is 100 per cent and an arrangement made without looking sits near zero, so the figure tells you how much of the true hue order you actually recovered. The chart breaks the same measure down tray by tray.

Expect a high number, and read the decimal place rather than the whole. The measure rewards getting the broad sweep of the circle right, so almost everyone who sorts carefully lands somewhere in the nineties, and the difference between one careful attempt and another lives in the fraction: ninety-nine and a half is a very different arrangement from ninety-five.

The three bands are cut against this test rather than against the clinic. The physical Farnsworth-Munsell test has published cutoffs, but they were measured on real Munsell caps under standardised lighting, and this version uses its own colour series on whatever screen you happen to be reading this on; borrowing those numbers would put an ordinary careful attempt in the bottom band. The boundaries here sit at 99.3 and 96 per cent, which over simulated attempts separates a very careful sort from an ordinary one and an ordinary one from a rushed one. Age matters too. Discrimination is at its best in early adulthood and declines gradually afterwards, so a score that looks unremarkable at fifty may be strong for that age.

The pattern of your errors carries more information than the total alone. The chart on your result page draws one spoke per cap, in that cap's own colour, pointing outward in proportion to how far it strayed. Inherited colour vision differences tend to produce errors concentrated along a particular axis of the circle — a bipolar cluster rather than a scatter — while acquired conditions and simple inattention usually spread errors around more evenly. A tidy circle with two opposite tufts sticking out looks quite different from a uniformly ragged one, and the shape is the part worth looking at.

This is a screening exercise, not a clinical examination. The genuine version is done with physical caps under a standardised light source, and no web page can control for your screen's calibration, its brightness, the angle you are viewing it from, a night-shift filter, or the lamp behind you. Fatigue and haste both cost points as reliably as any visual difference does. Treat a high score as a reason to try again in better conditions rather than a finding, and if you have a real concern about your colour vision, an optometrist can test it properly in a few minutes.

References

• Farnsworth, D. (1943). The Farnsworth-Munsell 100-Hue and dichotomous tests for colour vision. Journal of the Optical Society of America, 33(10), 568-578.
• Kinnear, P. R., & Sahraie, A. (2002). New Farnsworth-Munsell 100 hue test norms of normal observers for each year of age 5-22 and for age decades 30-70. British Journal of Ophthalmology, 86(12), 1408-1411.
• Verriest, G., Van Laethem, J., & Uvijls, A. (1982). A new assessment of the normal ranges of the Farnsworth-Munsell 100-hue test scores. American Journal of Ophthalmology, 93(5), 635-642.