Tritanopia · tritan dichromacy
Tritanopia (blue-yellow blind)
Without functioning short-wavelength S cones, blue ↔ green and yellow ↔ pink/purple get confused. Very rare.
- Missing cones
- S (short wavelength, blue)
- Inheritance
- Autosomal dominant (chromosome 7)
- Prevalence
- All blue-yellow types: fewer than 1 in 10,000
- Neutral point
- ~570 nm (yellow) looks gray
How it works
Tritanopia is a dichromacy caused by a variant in the S-cone photopigment (the OPN1SW gene on chromosome 7), leaving color to be judged with the L and M cones only. Because it is inherited in an autosomal dominant pattern rather than on a sex chromosome, it occurs about equally in men and women.
S cones are few in the retina and contribute almost nothing to the sense of brightness, so tritan confusion arises in hue rather than in brightness.
Blue-yellow discrimination can also weaken later in life when the lens yellows with age or with eye diseases such as glaucoma or diabetic retinopathy. Any new trouble telling colors apart calls for an eye exam.
What you see
Blue and green look like a similar teal, yellow shifts toward light pink or white, and purple draws close to red and pink. Red-green discrimination is relatively well preserved.
The table below shows the Machado model's tritan simulation. The tritan model has less research behind it than the protan and deutan models, so it may differ more from real experience.
| Color | Normal vision | Tritanopia (blue-yellow blind) |
|---|---|---|
| Red | #D7263D | #ED0031 |
| Orange | #F28C28 | #FF7579 |
| Yellow | #F2CD37 | #FFBCB1 |
| Green | #2E9E44 | #009A8A |
| Teal | #1A9E9A | #00A39C |
| Blue | #2F6BD8 | #008597 |
| Purple | #7E3FB2 | #755773 |
| Pink | #E86FA6 | #F76984 |
| Brown | #8B5A2B | #984F50 |
| Gray | #8C8C8C | #8C8C8C |
Simulation: Machado, Oliveira & Fernandes (2009) matrices at 100% severity. Results may differ from reality depending on your monitor and individual differences.
How common is it?
Blue-yellow color vision deficiency occurs in fewer than 1 in 10,000 people worldwide, at similar rates in men and women (MedlinePlus Genetics).
If you missed many tritan plates in an on-screen check, suspect night mode or a blue light filter first. Settings that reduce blue light directly erase the color differences on tritan plates. Limits of online tests
Easily confused colors
- Blue ↔ green, blue-green ↔ gray
- Yellow ↔ white/light pink, yellow ↔ lavender
- Purple ↔ red, orange ↔ pink
Everyday tips
- You may miss blue-coded cues (info badges, link colors). Check whether there's an underline or an icon.
- If tritan symptoms appeared suddenly or affect only one eye, they are probably not congenital — see an eye doctor.
- Try the “Blue/Yellow Filter (Tritanopia)” correction in your phone's color filters.