Legibility for everyone.
WHY IT MATTERS
Low contrast text is unreadable for many people, and for anyone in poor conditions.
WHAT AFFECTS IT
Text colour against its background Text size and weight Screen quality and brightness Ambient light
THE AMBIENT LIGHT POINT
A phone in direct sunlight loses most subtle contrast.
That is a common condition here, not an edge case.
WHAT TO CHECK
Body text against its background Text on images Placeholder text Disabled text Interface elements and borders
WHAT COMMONLY FAILS
Grey text on white, chosen because it looks refined Text over photographs Light weights at small sizes
WHAT TO DO ABOUT TEXT ON IMAGES
Add an overlay, or place text on a solid area.
WHAT TOOLS EXIST
Contrast checkers, which report whether a combination meets recognised thresholds.
WHAT TO ADOPT
A minimum standard, applied everywhere.
WHAT TO TEST
Outdoors, on a phone.