Free Color Blindness Simulator
Paste your colours or open a picture to see them as colour-blind people do, and find pairs that merge.
What is a Color Blindness Simulator?
This color blindness simulator shows a palette and pictures the way people with protanopia, deuteranopia, tritanopia and achromatopsia see them. It compares every pair of colours and lists the ones that become hard to tell apart for each type, so you can fix a palette before it reaches people who can’t read it.
Colours are simulated with Machado, Oliveira and Fernandes’ 2009 model, applied in linear light as the model intends, and achromatopsia as luminance only. Differences are measured with CIEDE2000, a formula built to follow how different colours look, so the pairs it flags are the ones people struggle with.
Key Features
Four Types of Vision
Protanopia, deuteranopia, tritanopia and achromatopsia side by side.
Pairs That Merge
Every colour pair compared, the closest flagged first.
Picture Simulation
Open a screenshot or photo and see it four ways.
Simulated Hex Values
Each colour’s simulated value to copy into mockups.
Named Palettes
Write each colour with its role, such as Error #dc2626.
Perfect for everyone
- Designers
- Data visualisation authors
- Front-end developers and accessibility reviewers
How to Use the Color Blindness Simulator
Paste your palette one colour per line, with a name if it helps, or open a screenshot of the interface. The swatches, simulated values and pair list update as you edit, so you can nudge a colour and watch a merged pair separate.
Paste the Palette
One colour per line, in hex, rgb() or hsl().
Compare the Rows
Each row shows a colour as each type sees it.
Read the Pairs
Pairs lists colours that merge, per type.
Check a Picture
Open a screenshot to see a whole screen.
Palettes, Seen Four Ways
Each row is a palette of the kind used for status messages, charts, maps and brands, including a few that fail. Each answer is this tool’s simulation, pair list or check, with differences measured in CIEDE2000.
“Error #dc2626 Warning #f59e0b Success #16a34a Info #2563eb Neutral #6b7280”
“Orange #e69f00 Sky blue #56b4e9 Bluish green #009e73 Yellow #f0e442 Blue #0072b2 Vermillion #d55e00 Reddish purple #cc79a7 Black #000000”
“Series A rgb(31, 119, 180) Series B rgb(255, 127, 14) Series C rgb(44, 160, 44) Series D rgb(214, 39, 40) Series E rgb(148, 103, 189)”
“#ff0000, #00ff00, #0000ff”
“Stop #e53935 Caution #fdd835 Go #43a047”
“Link hsl(217, 91%, 60%) Visited hsl(271, 81%, 56%)”
“Primary #2563eb Primary hover #2463e9 Accent #f97316 Accent light #fb923c”
“Low #1a9850 Low-mid #91cf60 Mid #ffffbf High-mid #fc8d59 High #d73027”
“primary, secondary, accent”
“Teal #008080 rgb(300, 0, 0) #008080”
The Four Simulated Types
Colour vision deficiency comes from a missing or shifted cone type in the eye. These are the four complete forms the simulator shows; milder, more common forms sit between them and typical vision.
Protanopia
No working red-sensitive cones; reds look darker and merge with greens.
“Which cones are missing?”
Deuteranopia
No working green-sensitive cones; reds and greens merge.
“Is red-green the most common kind?”
Tritanopia
No working blue-sensitive cones; blues and greens, and yellows and pinks, merge.
“Is tritanopia common?”
Achromatopsia
No colour vision at all; only lightness remains.
“What is left?”
How the Simulation Works
Simulating colour blindness means predicting what colour a person with a given deficiency perceives, then showing a colour that typical eyes see the same way. Each step below follows published colour science rather than a filter tuned by eye.
Into Linear Light
sRGB values are decoded to linear light first, because the cone model works on light, not on screen code values.
Machado Matrices
A 3 by 3 matrix per type, from Machado, Oliveira and Fernandes’ 2009 model, maps each colour to its dichromat equivalent.
Luminance for Achromatopsia
With no colour vision, each colour becomes the grey of the same relative luminance.
Comparing Pairs
CIEDE2000 then measures every simulated pair, and differences under 10 are flagged as hard to tell apart.
Fixing a Palette That Fails
When pairs merge, small changes usually fix them without abandoning the brand colours. Try one at a time and watch the pair list shrink, because a change that helps one type of vision can occasionally hurt another.
Separate Lightness
Make one colour of a merged pair clearly lighter or darker.
Shift the Hue
Move red toward orange-red and green toward blue-green.
Add a Second Cue
Pair colour with icons, labels, patterns or line styles.
Start From a Safe Set
Okabe–Ito and similar palettes are built to stay distinct.
Limit the Count
Fewer colours are easier to keep apart for everyone.
Accessible Colour Tips
Habits that keep colour from being the only way information gets across, in line with WCAG’s guidance on use of colour. They help people with typical vision too, on dim screens, in sunlight and in greyscale printouts.
Never Colour Alone
Pair status colours with an icon or word.
Label Chart Lines
Name series on the chart, not only in a legend.
Check Real Screens
Open a screenshot; small swatches hide problems.
Mind Thin Lines
Colour differences shrink on thin lines and small text.
Test Both Themes
Dark and light themes can fail in different places.
Who Uses a Colour Blindness Simulator
Anyone whose work uses colour to mean something, from a dashboard’s red and green to a map’s legend. With roughly one in twelve men affected, most large audiences include several people who see the palette differently.
Product Designers
Check status and alert colours before handoff.
Data Visualisation
Make sure chart series stay distinct.
Brand Teams
See how a palette holds up for every viewer.
Accessibility Reviews
Show stakeholders what a failing screen looks like.
Teachers
Check slides and worksheets for colour-coded content.
Colour Pitfalls
The patterns that most often leave colour-blind users guessing, and that the pair list tends to catch first. Most of them share a cause: two colours that differ in hue but not much in lightness.
Red Versus Green
The classic pair that merges for deuteranopia and protanopia.
Similar Lightness
Colours of equal lightness merge in achromatopsia.
Rainbow Scales
Rainbow colour maps hide differences for most types.
Hover-Only Changes
A colour shift alone may go unnoticed.
Trusting a Single Check
Simulation helps, but testing with real people matters most.