If one thinks about such things, there is no reason that either
hearing or the ability to perceive red from green are really required
intrinsically to fly an airplane.

But in one way the two groups have a conflict. Tower signal lights are
used for signalling aircraft that are NORDO, having red and green
lights. These are the very colors not separable by victims of the most
common type of colorblindness. Retiring the signal lights would be
beneficial to the colorblind, but devastating to the deaf.

In the modern digital world, neither audio nor colored lights provide
optimum interface with ATC. Each aircraft could be equipped with a data
link, and in nonaviation quantities very cheaply. However, everything
in a light aircraft costs stupid money because of the usual reasons and
really because pilots will pay it or not fly.