what is a CRT?
A CRT is a cathode ray tube. These were the first coloured screens used in glass cockpits. Most glass cockpits nowadays use LCD displays but the principle is the same.
I would draw attention to this fact; if an aeroplane's instruments cannot be safely interpreted by a pilot whose colour vision just meets current standards, then that aircraft is unairworthy.
The pilots who won the second world war, won it on black and white instruments.