The invisible phone number

1 · The crime

What goes wrong

A plumber's emergency number is pale blue on white. Standing outside with a flooded kitchen and a wet phone, nobody can read it.

2 · The law

If text is hard to see, it isn't there.

• Text needs a contrast ratio of at least 4.5:1 against its background (3:1 for large text). This is part of WCAG, the international accessibility standard.
• Contrast problems affect everyone in sunlight, older eyes and people with low vision.
• Information shown only in a photo of text can't be read by screen readers, search engines or translators.

3 · The tool

Check it yourself, for free

• WebAIM Contrast Checker (webaim.org/resources/contrastchecker).
• WAVE (wave.webaim.org) to scan a whole page for contrast and missing alt text.
• Your phone outdoors at full brightness: a quick real-world test.

4 · The fix

Step by step

1. Use your darkest text colour for body text and headings.
2. Check every text and background pair with a contrast checker and adjust until it passes.
3. Turn menus, prices and timetables in images into real text.
4. Give every meaningful image a short alt text describing it.