Well, if I was a pilot with colour blindness the first thing I would do is triple my loss of licence insurance and then sit back and wait.
This strikes me as far more cynical than it seems. If companies can be persuaded to fire or request resignation of such affected pilots then it stays a matter between the company and the pilot (and then the tribunal), on the other hand, if CASA issue new legislation that bars pilots with colour blindness, it is a whole new ball game.
Now we are in the area of compensation from CASA, loss of licence insurance from the insurers, who will, sure as night becomes day, having paid out, sue CASA for radically changing the risk and exposing the underwriters. Next, the pilots themselves will form a group and bring a class action against CASA for their loss of employment through no fault of their own.
So much easier if the companies let these pilots go 'voluntarily' before the legislation becomes law, so much less expensive than having to pay compensation etc.!
The letter quoted above is nothing to do with safety and all about money.