Yes, the removal of the colour green would be a degradation. It is one colour that is widespread in aviation. For example if you fail the colour green on CRT tubes the resulting screen displays become much more difficult to read and require careful discrimination of the resulting colours hues and shades available. This is acceptable on a temporary basis, but not as a normalization of that deviance.
I think you misunderstood the point about the rotating beacon. I was making the point that it cannot be relied upon to override the ability to make subtle discrimination of the colours used when taxiing under the circumstances I described. You brought it up as an example, and my response was that it could not be relied upon as evidence to provide for a normalization of deviance in the circumstances you described. It might be fine for light aircraft at a rural airfield. Not necessarily the case for a large busy airport with poor weather conditions.
Additionally there is simply no evidence that supports the idea that colour deficient pilots are unsafe.
Of course that's possibly because they have been eradicated to extinction in aviation by unjustly discriminative regulations. But not for pilots licensed in Australia where colour deficient pilots fly side by side with colour normals at all levels including international airline flying for the last 23 years. Yes! Colour deficient pilots fly 747s and A380s into Heathrow and elsewhere repeatedly and by day and night. Tell them they are unsafe
The fundamental problem here is who is "unsafe?" If you ask car drivers the same question, you would be hard pressed to find anybody who would tolerate such a notion, much less be told by somebody else that they are. Yet clearly many are. If a degradation is
less safe (and we agree that it is,) then the question becomes what degree of degradation is acceptable, and in what circumstances?
Collision avoidance is not by recognition of colour it's by relative bearing - ask any pilot. Sure aviation uses lots of colours but in a very adhoc way.
Really? Collision where? Under what circumstances? Collisions on the ground may well be caused by the poor ability to discriminate lighting. In the air the relative bearing is determined by the use of colour. Colour and the subtlety thereof, is used as an aid in establishing glideslope and safety areas on the ground. There are so many examples that arguing the relative merits of them all, simply detracts from the question as to whether an inability to discriminate between them all, is an acceptable compromise in standards. That colours are used in "a very adhoc way" rather suggests the need for the maintenance of a high discriminatory ability in the user rather than a lower one.
If there is going to be a normalization of deviance, and there already is in so many respects, then there are clearly going to be compromises to whatever degree. Such compromises already exist. For example many authorities permit the use of hypertension medication. Many of those same authorities have no stipulations as to the combinations of crew taking such medications. Is it safe therefore to have both pilots operating with controlled circulatory deficiences? Many would argue, yes! Some would argue, no! Similarly some authorities will not permit it in pilots certified within their own jurisdication, even though such pilots may regularly operate into their airports.
Visual acuity in the colour spectrum is obviously necessary and desirable. Any upheld standard in the ability to discriminate between not only colour, but the subtlety of colour, is in my experience essential. I can therefore see why there is a standard set at the level that it is. If an authority chooses to relax the standard (for example, for one pilot on a two man crew,) then the degradation becomes the acceptable standard by way of compromise.
There are many other examples of countries with different standards (including standards of safety) that have pilots
"flying 747's and A380's into Heathrow and elsewhere." There are examples of countries with higher standards. However that simply relects the compromise that any one authority is prepared to allow within the scope available to them.
Different countries, and in turn different authorities, set different standards in so many areas. Some will permit no deviance from the highest standards. Is that wrong? Perhaps in the eyes of those cannot meet those standards. Is it discriminatory? Yes, it is intended to be. However the discrimination is used to ensure the standard is met at the level required.
You hit the nail on the head - degradation may be acceptable if other factors provide a compensatory element.
However, there may not always be those compensatory factors, and should such a degradation be acceptable on a permanent basis rather than a temporary one?