Owl Listener Colour Independence
Design so that every piece of information conveyed by colour is also conveyed by something else — shape, text, pattern, position, or icon. 8% of men and 0.5% of women have colour vision deficiency. That's roughly 1 in 12 of your male users.
Core Principle
Colour can enhance meaning. Colour must never be the only carrier of meaning.
Common Failures
Status Indicators
- Bad: green dot = online, red dot = offline (colour only)
- Good: green dot + "Online" label, red dot + "Offline" label
- Better: green dot with tick + "Online", grey dot with x + "Offline"
Form Validation
- Bad: red border on invalid fields (colour only)
- Good: red border + error icon + error text message
- The error message does the real work — the colour is reinforcement
Data Visualisation
- Bad: line chart with 5 coloured lines, legend uses colour swatches
- Good: different line styles (solid, dashed, dotted) + labels + distinct colours that work in greyscale
- Good: bar chart with patterns (stripes, dots, solid) alongside colour
- Always test charts in greyscale — can you still read them?
Links
- Bad: links distinguished from body text only by colour
- Good: links are coloured AND underlined
- The underline is the accessible indicator — colour is the enhancement
Alerts and Badges
- Bad: red badge = urgent, yellow = warning, green = ok
- Good: red badge + "Urgent" label, yellow + "Warning" label, green + "OK" label
- Icons reinforce: ⚠ for warning, ✓ for success, ✕ for error
Maps and Diagrams
- Bad: regions coloured to show data (choropleth with no labels)
- Good: colours + patterns + values displayed on each region
- Good: interactive with values on hover/focus AND a data table alternative
Design Patterns
Double Encoding
Every colour meaning gets a second encoding:
- Colour + icon
- Colour + text label
- Colour + pattern or texture
- Colour + shape
- Colour + position
Accessible Colour Palettes
- Choose colours that are distinguishable in all types of colour vision deficiency (not just red-green)
- Use a colour blindness simulator to test your palette
- Blue and orange are generally safe for most types
- Avoid red/green as the only pair distinguishing two states
- Ensure sufficient contrast between adjacent colours in charts
Greyscale Test
Quick check: convert your interface to greyscale.
- Can you still use it?
- Can you distinguish all status states?
- Can you read the chart?
- Can you tell which fields have errors?
If any answer is no, colour is carrying meaning alone.
Assessment Checklist
- No information is conveyed by colour alone
- Status indicators use colour + icon + text
- Form errors use colour + icon + message
- Charts are readable in greyscale
- Links are distinguishable by more than colour
- Alert levels use colour + label + icon
- Data visualisations have patterns or labels alongside colour
- Interface passes the greyscale test