On Sunday, 12 November 2017 22:20:41 UTC, Steve Walker wrote:

Ah, fair enough. But each indicator should be labelled anyway. Coloured
indicators for each phase will still appear lit or not to a colour blind
person, so noworse for them than them all being white.


Not necessarily. I recently came across somebody who could not see red
at all. It was a sunny day and a glass ornament was casting a clear
spectrum on the wall. He pointed to the parts of the spectrum that he
could see. Red was simply not visible at all.

John