Color vision types explained
Protanopia vs Deuteranopia vs Tritanopia
Protanopia and deuteranopia are red-green color vision deficiencies, while tritanopia affects blue-yellow discrimination. The labels describe different cone-signal pathways, not three interchangeable filters.
protanopia
What is the difference between the three types?
Protanopia is a dichromatic red-green deficiency associated with loss of functional L-cone photopigment, so long-wavelength reds can also appear unusually dark. Deuteranopia is associated with loss of functional M-cone photopigment and creates a similar red-green confusion without the same protan darkening. Tritanopia is associated with the S-cone pathway and changes blue-yellow distinctions, including blue versus green and yellow versus pink. A protanopia simulation can reveal design collisions, but it is an approximation for review, not an eye test or diagnosis.
The comparison in brief
- Protanopia and deuteranopia both belong to the red-green group, but protanopia can reduce the apparent brightness of strong reds.
- Tritanopia belongs to the less-common blue-yellow group and creates a different set of color confusions.
- The suffix “-anopia” denotes loss of one cone-photopigment function; “-anomaly” describes an altered response rather than complete loss.
- A protanopia preview, a deuteranopia preview, and a tritanopia preview are separate review states; none predicts one person’s exact experience.
- Accessible design still needs labels, shapes, patterns, and measured luminance contrast because no simulation proves that a design is usable.
Protanopia, deuteranopia, and tritanopia compared
This table summarizes the classification used by the National Eye Institute and the American Academy of Ophthalmology’s EyeWiki. Individual perception varies, so treat the examples as review risks rather than a guaranteed visual recipe.
| Type | Cone pathway | Broad group | Common confusion risk | Design review priority |
|---|---|---|---|---|
| Protanopia | L-cone / long wavelength | Red-green | Red with green, plus dark red with black or brown | Check red brightness, value separation, labels, and outlines |
| Deuteranopia | M-cone / medium wavelength | Red-green | Red with green and nearby yellow-green or brown tones | Check semantic red-green pairs, shapes, and state text |
| Tritanopia | S-cone / short wavelength | Blue-yellow | Blue with green, purple with red, and yellow with pink | Check blue-green ramps, warm highlights, legends, and symbols |
Read the names before reading the simulated colors
Protanopia uses the prefix protan, which EyeWiki connects with the L-cone pathway. In practical review, protanopia deserves more than a generic “red-green” label because strongly red content may lose brightness as well as hue distinction. A dark red warning on black, a brown-red costume shadow, or a thin red chart line can therefore fail in a way that a bright simulation thumbnail does not immediately explain. When protanopia is the current review mode, compare relative lightness, not just the color name shown in a picker.
Tritanopia changes a different comparison axis
Tritanopia uses the tritan prefix for the S-cone pathway. The National Eye Institute describes confusion between blue and green, purple and red, and yellow and pink, with colors also appearing less bright. That means a blue-versus-green map, a yellow-versus-pink rarity scale, or purple damage on a red background needs a dedicated tritanopia check. Passing protanopia and deuteranopia review does not imply that the same design passes tritanopia review.
Separate simulation, screening, and diagnosis
A browser protanopia filter transforms pixels according to a model. It does not inspect a viewer’s retina, establish a medical history, control the display, or measure performance on a validated clinical test. Use a protanopia preview to ask whether two states, swatches, lines, or character regions collapse. Use a deuteranopia or tritanopia preview for the corresponding risk. Do not use any preview to tell a visitor which condition they have.
Turn the comparison into accessible design decisions
Start with the information task. If red means error and green means success, protanopia review should reveal whether the states remain distinct, but the fix should not be a more extreme red and green alone. Add an error icon, a success check, explicit status text, and a structural difference. For charts, combine hue with line style, marker shape, direct labels, or pattern. For characters, separate team, power, or rarity signals with silhouette, emblem, value, and material treatment.
A practical protanopia review checklist
Run the checklist on the original design and all three previews. The repeated protanopia pass is deliberate: it keeps the review tied to decisions rather than to an attractive filtered screenshot.
- protanopia: Compare every red semantic state with its green counterpart and read the labels without color.
- protanopia: Inspect strong reds against black, charcoal, dark brown, and deep green for lost brightness.
- protanopia: Zoom out to the smallest real chart, badge, avatar, or character size.
- protanopia: Convert the composition to grayscale and confirm the focal order still makes sense.
- protanopia: Give errors, warnings, success states, and selected states a text or icon cue.
- protanopia: Use line style, marker shape, pattern, or direct labels in charts and maps.
- protanopia: Check focus, hover, active, disabled, and visited states independently.
- protanopia: Measure text contrast rather than judging a simulated screenshot by eye.
- protanopia: Measure essential icons, boundaries, and control states where non-text contrast applies.
- protanopia: Compare the protanopia result with deuteranopia instead of assuming one red-green view is enough.
- protanopia: Run a separate tritanopia pass for blue-green and yellow-pink collisions.
- protanopia: Test light and dark themes because a safe distinction can disappear after inversion.
- protanopia: Review image overlays, subtitles, captions, and text baked into artwork.
- protanopia: Keep names or legends visible when a palette swatch carries a category.
- protanopia: Ask a person to complete the task; do not ask only whether the colors look different.
- protanopia: Record the tested state, background, HEX values, date, and any unresolved risk.
A five-step color-vision review workflow
The sequence combines simulation, contrast measurement, redundant cues, and a final task check. It works for interfaces, illustrations, charts, and color-coded game states.
1. Name the meaning
List every place where color carries status, identity, order, rarity, team, or action before opening a protanopia preview.
2. Simulate separately
Review protanopia, deuteranopia, and tritanopia one at a time, and note exact pairs or regions that merge.
3. Add another cue
Use text, shape, pattern, position, line style, border, or icon so the meaning survives without hue.
4. Measure contrast
Check the real text and essential graphic pairs; do not treat a protanopia screenshot as a contrast calculation.
5. Test the task
Ask whether a person can identify, compare, navigate, or act correctly, then document remaining limitations.
What the official sources establish
These sources define classification and accessibility boundaries. They do not certify a particular simulation as a diagnosis or guarantee that one palette works for everyone.
- The U.S. National Eye Institute lists 4 red-green types and 2 blue-yellow types. It says protanopia and deuteranopia both prevent red-green distinction, while tritanopia affects blue-green, purple-red, and yellow-pink pairs. National Eye Institute: types of color vision deficiency
- The American Academy of Ophthalmology’s EyeWiki maps protan, deutan, and tritan to L-, M-, and S-cones. It explains that “-anopia” denotes complete loss of one cone-photopigment function. AAO EyeWiki: color vision classification
- WCAG 2.2 Success Criterion 1.4.1 says color must not be the only visual means of conveying information, indicating an action, prompting a response, or distinguishing an element. W3C: Understanding Use of Color
- WCAG 2.2 Level AA sets a 4.5:1 minimum for normal text and 3:1 for large text. Its guidance treats these as thresholds, so 4.499:1 does not round up to a pass. W3C: Understanding Contrast Minimum
Color is not used as the only visual means of conveying information
NEI · AAO · W3C
Primary and official sources
Test the design, then verify the numbers
Protanopia, deuteranopia, and tritanopia FAQ
Is protanopia the same as red color blindness?
Protanopia is a red-green dichromatic deficiency associated with loss of functional L-cone photopigment. The shorthand “red-blind” is incomplete because perception is not simply an image with red pixels removed. Protanopia can also make long-wavelength reds appear darker and create confusions with greens, browns, or black. Use the full term and describe the task-specific risk.
Why do protanopia and deuteranopia simulations look similar?
Both affect red-green discrimination, so many transformed color relationships converge in similar ways. Protanopia is linked to the L-cone pathway and can darken strong reds; deuteranopia is linked to the M-cone pathway without the same protan brightness effect. Keep both review modes because a small difference can matter in dark themes, charts, costumes, and warning states.
Does a protanopia simulator prove that a palette is accessible?
No. A protanopia simulator is a modeled preview. It cannot diagnose vision, represent every severity, measure text contrast, confirm keyboard focus, or prove that a user understands the task. Combine protanopia review with deuteranopia and tritanopia checks, WCAG contrast measurement, redundant visual cues, and real task testing.
Should every red and green pair be removed?
No. WCAG does not ban red and green or discourage color. It requires that color not be the only way important information is communicated, and it sets contrast requirements for text and essential graphics. A red-green pair may remain when labels, icons, shapes, patterns, value contrast, or position provide a reliable second cue under protanopia review.