Bret Ludwig wrote:

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.

actually, no, you are wrong; the two colors most commonly
confused by the most common type of colorblindness (I presume
you are refering to protanomalous vision) are in practice
the white and green lights; and if you remember what these
mean in flight -- which most pilots don't :-) -- you'll see
that it would not be a problem;

besides, why would you want to 'retire' one system or the
other? the light gun is probably the least expensive piece
of equipment in the tower, lasts for ever, and is easily
operated -- they even have a placard to remind the controler
using it the meaning of the signals -- because many controlers
don't remember either :-)

--Sylvain