Hang on, we're not making the point here that colours don't matter, are we?
Yes we are (or at least I am).
What matters is a whether a person has the ability to perceive readily the
meanings of the real-life signals, symbols and indications that are coloured, or depend on the differences between colours, and are necessary for the safe performance of duties.
Don't the focus on the means; focus on the ends.
The conga line of medical zealots and experts with their snout in the CVD industry trough focus on the means: There are coloured lights with meanings. Therefore a pilot with an inability to perceive the colours of those lights is scary-dangerous.
Objective people focus on the ends: Does a pilot perceive readily the meaning of real-life signals, symbols and indications that are coloured, or depend on the differences between colours, and are necessary for the safe performance of duties. If a candidate with CVD perceives, as efficiently and effectively as candidates without CVD, the meaning of those real-life signals, symbols and indications, there is no objective safey basis on which to discriminate against the candidate with CVD.
And we know what the first-hand, real-life evidence shows.