Blue-Yellow Color Blind Test (Tritanopia)
Read the hidden number in each dot plate to screen for tritan (blue-yellow) colour vision deficiency.
Blue-Yellow (Tritan) Plate Test
Each plate is a mosaic of dots hiding a number. The figure and background differ only along the blue–yellow axis at matched brightness — so a tritan deficiency makes the number hard to read.
- •View on a screen at normal brightness with any blue-light / night filter turned off.
- •Tap the number you see. If you truly can't make one out, use “I can't see a number”.
- •Go with your first impression — don't over-stare at a plate.
Understanding Blue-Yellow Color Blindness
Blue-yellow colour vision deficiency — clinically called tritan deficiency — comes from the short-wavelength (S) cones, the rarest of the eye's three cone types. S-cones are most sensitive to blue light around 420 nm and make up only about 2% of all cones. Because there are so few of them to begin with, damage or a genetic change affecting them shifts how you tell blue from green and yellow from pink or grey.
There are two degrees. In tritanopia the S-cones are essentially absent or non-functional, so the blue-yellow axis collapses. In tritanomaly the S-cones work but are shifted or reduced, giving a milder, partial loss. Inherited tritan deficiency is extremely rare — under 0.01% of people — but a mild blue-yellow shift acquired later in life is much more common than most people realise.
Tritanopia
Complete blue-yellow color blindness. Blues may appear greenish, and yellows may appear violet or light gray.
Tritanomaly
Reduced blue sensitivity. Colors may appear slightly shifted, with difficulty distinguishing blue from green.
This distinction matters because a blue-yellow change is one of the earliest warning signs of several eye and systemic diseases. Unlike red-green deficiency, which is almost always something you're born with, a new or worsening tritan problem is worth having a professional check.
Symptoms of blue-yellow deficiency
Tritan deficiency is subtle, and many people live with a mild form without ever naming it. The most reliable clue is confusing specific colour pairs that sit along the blue-yellow confusion line:
- Blue looks green (and vice-versa). A blue-green teal, turquoise, or a navy garment can be hard to place — is it blue or green?
- Yellow fades to grey, pink or lilac. Yellows can look washed-out or beige; pale yellow and light grey become almost the same.
- Violet and purple read as plain blue. The red component in purple is lost, so purple flowers or lighting look simply blue.
- Trouble in low light. Blue-yellow discrimination weakens further at dusk or in dim rooms, when cones are least active.
- Pastel and muted tones are hardest. Saturated colours may be fine while soft, desaturated shades — exactly what this test uses — get confused.
What causes it — inherited vs acquired
Inherited (congenital) tritan deficiency
The inherited form is caused by changes in the OPN1SW gene on chromosome 7. Because chromosome 7 is an autosome — not a sex chromosome like the X that carries red-green genes — inherited tritan deficiency affects men and women equally. It is present from birth, stable over life, and very rare (roughly 1 in 10,000).
Acquired blue-yellow loss
Far more blue-yellow difficulty is acquired later in life. The blue-yellow pathway is especially fragile, so it is often the first to show damage. Common contributors include natural aging (the lens yellows and absorbs blue light), glaucoma, diabetic retinopathy, optic neuritis and other optic-nerve disease, and certain medications. A blue-yellow change appearing in one eye, or getting worse, is a reason to see an eye doctor.
How it affects daily life
Because pure tritan deficiency is rare and often mild, its impact is usually smaller than red-green deficiency — but it shows up in specific situations:
- Reading charts and maps. Blue-vs-green regions on transit maps, weather radar, or data dashboards can blur together.
- Buying and matching clothes. Telling navy from black, or teal from green, is a common everyday frustration.
- Cooking and freshness cues. Judging ripeness or doneness by subtle yellow-to-brown shifts can be less reliable.
- Screens and UI. Blue links, status colours, and pale-yellow highlights may not stand out as designers intend.
- Gardening and nature. Purple and blue flowers may look identical; yellowing leaves are harder to spot early.
How this online test works — and what it can't tell you
- How the plates are built. Every plate is generated in your browser as a dot mosaic. The hidden digit and the background are placed on opposite sides of the blue–yellow (tritan) confusion axis at deliberately similar luminance, with a small random brightness jitter per dot — so the number can't be read from brightness alone, only from blue–yellow discrimination.
- Screens under-represent blue. Standard sRGB displays cover only part of the blue-violet range the tritan axis needs, and every panel renders blue differently. That makes an online blue-yellow screen inherently less reliable than a red-green one — treat a borderline result as “worth checking”, not a diagnosis.
- It can't separate tritanomaly from tritanopia. Like most online plate tests, this one flags that a blue-yellow difficulty may exist — it does not measure its exact type or severity. That requires a clinical arrangement test (Farnsworth D-15) or the anomaloscope-style Cambridge Colour Test.
- Acquired vs inherited. Inherited tritan defects are extremely rare (<0.01%). Blue-yellow trouble far more often appears with age, medication, or eye disease (glaucoma, diabetic retinopathy). A new or one-sided blue-yellow change is a reason to see an eye doctor, not just retake a test.
- Not for official clearance. No online test — including this one — is valid for aviation, military, maritime, or occupational medical certification.
Sources
- National Eye Institute (NEI) — Overview of all color blindness types including Tritanopia
- American Academy of Ophthalmology (AAO) — Clinical information on blue-yellow color vision deficiency
- National Health Service (NHS) — Causes and management of colour vision deficiency including acquired forms
- Colour Blind Awareness — Prevalence and types of color vision deficiency
- MedlinePlus Genetics — OPN1SW gene — The blue-sensitive opsin gene on chromosome 7 behind inherited tritan deficiency
Frequently Asked Questions
Related Tests
Ishihara Test
Classic color blind test with 14 or 38 Ishihara plates.
Cambridge Color Test
Computerized test using Landolt C rings to screen for all types of color blindness.
Farnsworth D-15 Test
Arrange 15 colored caps to screen for protan, deutan, and tritan color vision deficiency.