Not relying on hue.
HOW COMMON IT IS
Common enough that a meaningful proportion of any audience is affected.
WHAT IT MEANS
Certain colour pairs are indistinguishable.
Red and green most often.
WHAT FAILS
Status shown only by colour Chart series distinguished only by colour Required fields marked only in red Links distinguished from text only by colour
WHAT TO DO INSTEAD
Pair colour with something else: text, an icon, a pattern, position, underlining.
WHAT TO DO ABOUT LINKS
Underline them within body text.
WHY
Colour alone is insufficient, and underlining is the recognised convention.
WHAT TO DO ABOUT CHARTS
Label series directly, or vary pattern as well as colour.
WHAT TO DO ABOUT STATUS
Include a word.
WHAT TO TEST
View the interface in greyscale.
WHAT THAT REVEALS
Everything depending on colour alone.
WHAT TO ALSO CHECK
That contrast remains adequate in greyscale.
