Anomalous trichromacy · Red–green
Deuteranomaly Simulated in sRGB
The medium-wavelength cones work, but their sensitivity is shifted toward the long-wavelength cones, so the green signal is weaker than it should be. Like deuteranopia, it is inherited on the X chromosome, so it is far more common in men than in women. It is the most common color vision deficiency, affecting about 1 in 20 men of European descent.
- Category
- Anomalous trichromacy
- Type
- Red–green
- Cones
- M cones shifted
- Simulation
- Machado et al. (2009)
Live lab
Everyday interfaces with deuteranomaly
Four everyday interfaces, or an image of your own, simulated as you watch. Drag the divider, change the severity, and turn on the fix to see the same interface designed so color is never the only clue.
The live lab needs JavaScript. The sections below show the same simulation, color by color.
A line chart of weekly sign-ups in four channels, told apart by color.
The same scene through all nine types, each at its usual severity.
- Closest pair
- Typical vision
- Deuteranomaly
- Verdict
ΔE2000 between the two key colors drawn closest together. Under 5 is too close for thin lines and small marks; 10 or more is safe at any size. A rule of thumb, not a standard.
With the fix, words, icons, numbers and patterns carry the meaning too, so the scene still reads even where two colors stay close.
A photo has no key colors to compare, so the lab simulates every pixel instead. Save the result to share it.
Everyday colors
How deuteranomaly changes common colors
Greens, yellows, oranges and reds lose some of their difference, and muted greens, browns and pinks suffer most. Many people with it are only mildly affected and may not know.
Each chip is the color on the left and the simulation on the right. Open one for its full page.
Simulated at severity 0.6 on the 0 to 1 scale of Machado et al. (2009), a moderate case; the range is shown below.
Severity
From mild to severe
Deuteranomaly is a range, not one condition. Each strip is twelve hues at one severity; at 1.0 it matches deuteranopia.
Typical vision
Severity 0.2
Severity 0.4
Severity 0.6 (used on this page)
Severity 0.8
Severity 1.0 (deuteranopia)
Confusion lines
The lines colors drift along
This map holds every color's hue and saturation, with the spectrum round its curved edge. Each straight line runs through colors that deuteranomaly draws together; only lightness separates them. All the lines meet at one point, outside the diagram, below and to the right of it. Deuteranomaly shares these lines with deuteranopia, but colors along a line can still be told apart a little, more so the milder it is.
Seen as one hue
The numbers are the closest pair in each group, typical vision first.
The lines meet at points worked out from the cone measurements of Smith and Pokorny; strictly those belong to a corrected version of this diagram, so the lines here are close, not exact. Smith & Pokorny 1975
- Confusion lines
- The line through white
- White (D65)
- Neutral point 500 nm
- sRGB gamut
Confusions
Colors deuteranomaly draws together
CSS named colors that are far apart to typical vision and drawn closest together once simulated. The difference left is small, so do not tell these apart by color alone.
The cones
M cones shifted toward L
Each curve is how strongly one cone pigment absorbs light across the spectrum, peaking at about 419, 531 and 558 nm. The faint curve is the normal M pigment; the solid one is where this page's simulation puts it, 12 nm toward L, following Machado et al. (2009). In real deuteranomaly the anomalous pigment peaks 4 to 12 nm from the normal L pigment. Below the curves, the visible spectrum as typical vision and as this type see it.
- S
- 0.00
- M
- 0.99
- L
- 0.99
Typical vision
Deuteranomaly
The curves are the visual pigment template of Govardovskii et al. (2000) at the peaks Dartnall, Bowmaker and Mollon measured in human eyes. They show the pigments themselves; at the cornea the eye's lens and macular pigment shift them. Govardovskii et al. 2000 · Dartnall et al. 1983 · Machado et al. 2009 · Sharpe et al. 1999
Genes
How it is inherited
The genes behind it, where they sit, and the odds of passing it on. Pick the parents to see a Punnett square: each square is one chance in four.
- Genes
- OPN1MW, OPN1LW
- Where
- Xq28
- Inheritance
- X-linked recessive
- What changes
- A hybrid of the M and L genes makes an anomalous, L-like pigment, peaking 4 to 12 nm from the normal L pigment.
The calculator needs JavaScript.
If the parents are
X* is an X chromosome carrying the change. A son has one X, from his mother; a daughter needs it on both. Carriers usually see color normally.
Diagnosis
How it is tested
A screening test says that something is different; a diagnostic one says what. Only an eye care professional can diagnose a color vision deficiency. Plates on a screen, including this site's, show the idea but cannot diagnose.
| Test | What it is | For this type |
|---|---|---|
| Ishihara plates | Plates of colored dots hiding numbers: the standard screen for red–green deficiency. It cannot grade severity or tell dichromats from anomalous trichromats. Ishihara instructions | Detects it |
| HRR plates | Plates with shapes instead of numbers. They screen for red–green and blue–yellow loss and grade it as mild, medium or strong. Bailey et al. 2004 | Detects and grades it |
| Farnsworth D-15 | Fifteen colored caps to put in order. Almost every dichromat fails; many people with a mild anomaly pass. The pattern of errors shows the axis. Birch 2008 | Partly |
| Farnsworth–Munsell 100 Hue | Eighty-five caps in four trays, scored for errors. Good for measuring discrimination and following an acquired loss; weak at telling inherited types apart. Birch 1989 | Partly |
| Nagel anomaloscope | Match a yellow light with a mix of red and green. The reference test for red–green deficiency: it tells protan from deutan and dichromacy from anomalous trichromacy, and grades severity. Birch 2008 | Detects and grades it |
| CAD test | A computer test that measures red–green and yellow–blue thresholds against moving luminance noise, and reports severity in standard units. Rodriguez-Carmona et al. 2012 | Detects and grades it |
| Cambridge Colour Test | A computer test: find the gap in a C drawn in colored dots among dots of random lightness. It measures thresholds along the protan, deutan and tritan axes. Regan et al. 1994 | Detects and grades it |
Status colors
Red, amber and green
A traffic-light status set leans entirely on hue. Give each state a word or an icon too, as WCAG 1.4.1 asks.
WCAG 1.4.1 Use of Color- Error
- Warning
- Success
Top: typical vision. Bottom: deuteranomaly. The closest two status colors end up ΔE2000 21.2 apart.
Your palette
Check your colors
Paste a palette, or start from one below. The bars show the closest pair under every type; the table shows every pair under the one you pick.
The checker needs JavaScript.
Hex codes, separated by commas or spaces, up to 12. Skipped:
Closest pair under each type
Too close Borderline Distinct
Design for it
Designing so it does not matter
- Never let color carry meaning alone: add a label, an icon, a pattern or a position.
- Separate colors by lightness as well as hue, so they stay apart in every simulation.
- Keep text contrast at 4.5:1 or more, and 3:1 for icons and the edges of controls.
- Check designs with a simulator before you ship them.
Simulate a whole page in the Color Blindness Simulator, or check a pair in the Contrast Checker.
Other types