Professional Red-Green Color Blind Test (Ishihara-style)

This interactive Ishihara-style test generates 20 randomized dot plates to evaluate how well you distinguish red and green hues. The tool adapts plate difficulty in real time, tracks your accuracy and response speed, and summarizes performance with clear metrics and visuals—right in your browser.

Ishihara Red-Green Color Discrimination Test

This test evaluates your ability to distinguish red-green colours using Ishihara-style plates.

Test Instructions

Look at the circle and identify the number formed by the coloured dots
Type the number you see in the input field and click Submit
If you cannot see a number, you can click Skip
The test adapts to your ability — it becomes harder with correct answers
Complete all 20 plates for a comprehensive assessment
Ensure proper lighting and disable any colour-enhancing or -adjusting features on your screen
The test measures your response time for each plate

Difficulty: Medium

Plate 1 of 20 0 Correct

Test Results

Score: 0/20

Share this?

How to Use the Test

Prepare your screen: Turn off Night Shift, blue-light filters, or any “warm” color modes. Keep brightness moderate.
Set your environment: Use neutral room lighting, avoid glare, and sit about arm’s length from the display.
Check zoom: Keep the browser at 100% so plates are rendered at the intended size.
Start: Click “Start Test” to begin the sequence of plates.
Respond: Type the number you see in the circle. If none is visible, click “Skip.”
Complete all 20 plates: The difficulty automatically adjusts based on your answers.
Review results: At the end, you’ll get your score, the highest difficulty you reached, and detailed feedback (for free, no e-mail, no registration).

Features of The Test

20 adaptive Ishihara-style plates per session
Seven difficulty levels: Very Easy to Extreme
Real-time adaptive staircase that adjusts difficulty with every answer
Extreme mode with micro-refinements in hue and saturation
Procedurally generated dot fields and embedded shapes (no repeats)
Randomized numbers between 1 and 99
Per-plate response time tracking
Instant feedback after each submission
Skip option for uncertain answers
Live progress bar and score counter
Difficulty indicator with labels and dot markers
Performance analysis by difficulty level
Mastery percentage calculation
Final results with score, accuracy, median response time
Headline interpretation based on smallest resolved hue difference
Detailed results with color swatches and plate metadata
Tailored performance summary and estimated threshold
Data quality checks (fast/slow responses, low accuracy, few trials)
Responsive interface for desktop, tablet, and mobile
Restart button to instantly retake the test

Why It Works for Color Blindness Recognition

The test challenges the L–M cone pathway of the eye, which is where red–green deficiencies (protan and deutan types) occur. By presenting numbers hidden in randomized dot fields and progressively narrowing the hue difference (Δh) between red and green, it stresses the very contrast most affected by red–green color vision anomalies.

The adaptive staircase ensures each user is pushed toward their perceptual threshold, while randomized plate generation prevents reliance on memory. This makes the tool effective at highlighting typical recognition patterns seen in individuals with and without red–green color blindness.

Professional Red-Green Color Blind Test (Ishihara-style)

Number 30 plate from the test

Frequently Asked Questions

Why are Ishihara plates effective for detecting red–green color blindness?

Ishihara plates exploit the fact that people with protan (L-cone deficiency) or deutan (M-cone deficiency) have reduced sensitivity to differences along the red–green axis of color space.

By embedding numbers in dot patterns where only chromatic contrast (ΔL/ΔM signals) defines the figure, and luminance cues are minimized, these plates selectively stress the pathways most affected by red–green color vision deficiency.

How does this test differ from clinical Ishihara books?

Clinical Ishihara plates are printed with precisely calibrated inks to control spectral reflectance under standardized lighting (usually CIE Standard Illuminant C). Online tests, while useful for screening, depend on display gamut, gamma, and calibration. The algorithm here reproduces the principle—randomized pseudo-isochromatic dots with controlled Δh along the red–green axis—but the absolute colorimetry cannot be standardized across devices.

Why does this tool use an adaptive staircase rather than fixed plates?

In psychophysics, adaptive staircases (e.g., 2-up/1-down or 3-up/1-down rules) efficiently converge toward an observer’s threshold—often around 70–80% correct—by dynamically adjusting difficulty. This avoids wasted trials that are too easy or too hard, and yields a finer-grained estimate of the minimum hue separation (Δh) a user can resolve.

Can this type of test detect tritan (blue–yellow) deficiencies?

No. Ishihara plates and red–green adaptive tests target the L–M pathway. Tritan defects involve the S-cone system (blue–yellow axis) and require specialized stimuli designed to vary along S/(L+M).

Tools like the HRR plates or Farnsworth D-15 test are more appropriate for assessing tritanomaly or tritanopia.

What does a “Δh threshold” represent scientifically?

Δh refers to the hue angle difference in color space (here approximated with HSL/HSV, but clinically measured in CIE L*a*b* or LMS cone coordinates).

The smaller the Δh that an observer can reliably discriminate, the finer their chromatic resolution along that axis. For typical trichromats, thresholds are only a few degrees, while red–green deficient observers may require much larger Δh values.

References

Bento-Torres et al. (2016), *Psychophysical Evaluation of Congenital Colour Vision Deficiencies* – shows that protan and deutan individuals have reduced color discrimination thresholds along the red–green axis, particularly when assessed using Farnsworth–Munsell and Mollon–Reffin paradigms.
Wikipedia – *Ishihara test* overview – the classic pseudoisochromatic plates embed numbers in dot patterns designed to be visible only to observers with normal red–green color discrimination, forming the basis for modern screening tools.
Fanlo-Zarazaga et al. (2024), *Validation of a New Digital and Automated Color Perception Test* – compares digital, automated tests across red, green, and blue discrimination axes with traditional Ishihara and Farnsworth–Munsell tests, underscoring the emerging validity of screen-based color-vision testing.