Loading page
About this tool
See your palette with all colour removed and check every pair against the WCAG 3:1 and 4.5:1 contrast thresholds.
Achromatopsia Palette Simulator converts a palette to true greyscale and scores every pair of colours with the WCAG 2.x contrast formula, (L1 + 0.05) / (L2 + 0.05), so you can see which swatches survive on their luminance alone. Three conversions are offered — WCAG relative luminance on linearised sRGB, the CSS grayscale() filter matrix, and Rec. 601 luma — because they produce visibly different greys from the same colour. It is for designers checking that a chart, status badge or state colour still communicates when hue carries no information at all.
Open Achromatopsia Palette Simulator on AltFTool — it loads instantly in your browser.
Add your input to the workspace.
Adjust the options until the result looks right.
Copy or download the output and put it to work.
Uses the sRGB transfer function from IEC 61966-2-1, not a naive channel average.
Ranks all colour pairs worst first against the 3:1 and 4.5:1 WCAG thresholds.
Shows where the CSS filter and Rec. 601 luma disagree with true relative luminance.
Achromatopsia is the complete absence of colour vision, in which only lightness differences are perceived. Complete rod monochromacy is rare — roughly 1 in 30,000 people — but the same flattening happens to everyone on a greyscale print, an e-ink screen or a display washed out by sunlight.
No. The WCAG contrast formula is built on relative luminance and ignores hue completely, so a pair that reaches 4.5:1 in colour reaches the same ratio in greyscale. What disappears is any distinction that was carried by hue at similar lightness, such as a red and a green of the same luminance.
Linearise each channel with the sRGB transfer function, combine them as 0.2126 R + 0.7152 G + 0.0722 B, then re-encode. Applying those weights directly to the gamma-encoded values — which is what CSS grayscale() does — gives a different, usually darker, result for saturated colours.
WCAG 2.1 requires 4.5:1 for body text (SC 1.4.3), 3:1 for large text and for user interface components and graphical objects (SC 1.4.11), and 7:1 for enhanced AAA text. Two swatches below roughly 1.5:1 read as the same tone and should never be the only way a state is signalled.