Folks,
Back in the 1990s, Dr. Pape represented IAOPA at an ICAO medical standards conference in Warsaw, a conference where colour vision was "the" major subject.
At the time, the proponents of ever more restrictive standards were shouting the odds about the use of standard colours in glass cockpits, and how this settled the argument, once and for all time, of the nee for "standard" colour vision of pilots.
This was anticipated, we ensured Dr. Pape was equipped with a useful set of pictures of the glass cockpits of a B767, where the screens had lost the colour ( I forget the actual, defect) and became grayscale screens.
Dr. Pape was able to point out that the MEL operational limitations for the defect were precisely zero, the aeroplane was certified to operate without limitation in the absence of colour.
Quite simply, the point is that the need for standard colour vision has always been assumed, it has never been proven.
Put another way, it has never been proven that a CVD pilot in any way is a threat, and therefor increases the risk of the operation.
Tootle pip!!