Monochromacy · Complete
Blue-cone monochromacy Simulated in sRGB
Only the short-wavelength cones and the rods work; neither the long- nor the medium-wavelength cones do. It is inherited on the X chromosome, so almost everyone with it is male. It affects about 1 in 100,000 people.
- Category
- Monochromacy
- Type
- Complete
- Cones
- S cones only
- Simulation
- S-cone signal only
Live lab
Everyday interfaces with blue-cone monochromacy
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
- Blue-cone monochromacy
- 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 blue-cone monochromacy changes common colors
Daylight vision runs on one cone type, so hue is lost: blues look bright, and reds and oranges very dark. It comes with reduced sharpness of vision and sensitivity to light.
Each chip is the color on the left and the simulation on the right. Open one for its full page.
Each color is shown as the gray of its S-cone signal alone. At dusk, rods and S cones together give a little color discrimination, which the simulation leaves out.
Lightness
Only lightness is left
With only S cones and rods, lightness follows the S-cone signal: blues look light and reds very dark. Here are the everyday colors, darkest first; those within 3 L* of each other are the same gray.
Confusions
Colors blue-cone monochromacy confuses
CSS named colors that are far apart to typical vision but nearly identical once simulated. Never tell these apart by color alone.
The cones
S cones and rods only
Each curve is how strongly one cone pigment absorbs light across the spectrum, peaking at about 419, 531 and 558 nm. Only the S cones and the rods work, so long and medium wavelengths cannot be compared. Below the curves, the visible spectrum as typical vision and as this type see it.
- S
- 0.00
- M
- —
- L
- —
- Rods
- 0.37
Typical vision
Blue-cone monochromacy
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
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
- OPN1LW, OPN1MW
- Where
- Xq28
- Inheritance
- X-linked recessive
- What changes
- The L and M cones both fail: a deletion removes the region that switches both genes on (the locus control region), or the pair is cut to one gene that a mutation then disables.
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, which is why almost everyone with it is male.
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 |
|---|---|---|
| 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 | Detects it |
| 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 | Partly |
| ERG and genetic testing | An electroretinogram shows cone responses absent or much reduced, with rods near normal; a genetic test confirms the gene. Blue-cone monochromacy is told apart by its working S cones. GeneReviews: achromatopsia | Detects 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: blue-cone monochromacy. The closest two status colors end up ΔE2000 5.5 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