Farnsworth D-15 Test
A free, screen-based colour-arrangement tool based on the Farnsworth D-15 method: order the caps so each colour blends smoothly into the next, starting from the fixed reference cap. The way the order breaks hints at the confusion axis.
Tap a cap to pick it up, then tap another to swap them. Start from the fixed cap on the left and work toward the most similar colour each time.
What the Farnsworth D-15 measures
The D-15 is an arrangement test. You place 15 coloured caps in order of hue, forming a smooth loop around the colour circle. People with normal colour vision manage this easily. People with a colour deficiency put certain caps out of order, specifically, they treat caps that sit on opposite sides of their "confusion axis" as if they were neighbours.
Plotting those swaps produces diagonal lines across the colour circle. The direction of those lines tells the clinician whether the deficiency is protan, deutan or tritan, and whether it is strong enough to matter. That makes the D-15 a useful complement to Ishihara plates, which screen quickly but don't grade severity as well.
Online vs clinical D-15
This is an original, screen-based tool based on the Farnsworth D-15 method. It uses generic on-screen hues, not the official calibrated Munsell caps, and is not affiliated with, or endorsed by, any test publisher. A clinical D-15 uses physical Munsell caps under standard lighting, which a screen can't reproduce, so treat this version as a demonstration and a rough screen, not a diagnosis. For colour-critical decisions, take the physical test with an optometrist. You can also try the Ishihara-style plate test or the anomaloscope explainer.
Frequently asked questions
What is the Farnsworth D-15 test?
Is the D-15 better than the Ishihara test?
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