Use symbols as well as colour
If you are using red to signal “warning,” or “caution,” and green to signal “approval” or “correctness” consider adding a symbol to make sure colour-blind users can still understand the message.
Example of how to use colour and symbols to improve accessibility
Traffic lights use red and green, but the position of the lights communicates “stop” or “go”, even if the colours cannot be seen.
Example of how traffic lights convey meaning through colour and position
Appearance for someone with red-green colour-blindness
Colour should never be the only method of communication
When the use of red and green is unavoidable, for example, RAG (red, amber, green) ratings, make sure that colour is not the only method of communication.
Consider representing RAG ratings in the same way as the previous examples, with a secondary method of communication.