You must not rely solely on colour to indicate something.
If you have to use colour to indicate something you must also provide a text description.
"Dangerous areas are indicated in red on the map."
If someone cannot see red (for example, if they are red/green colour blind) then they wouldn't be able to tell where the dangerous areas are. A possible solution might be to add the word 'Danger' to the areas.
"The green bar on the chart represents our budget for next year."
Consider labelling the chart or referring to the bar differently (for example, the second bar from the bottom).
Accessibility - this standard is mandatory for accessibility reasons.
You can't rely on people seeing the same colours as you. For example: