(in said:
Does anyone know why video connectors have impedance 75 Ohms not 50 or
any other number Ohms?
Why is 75 Ohms better than 50 Ohms for video signals?
Better colour rendering 75 ohms is violet-green-brown, while 50 ohms is
only green-black-brown. Violet and green are complementary, so you can
get any colour along that axis by mixing. Brown is low-brightness yellow
(yellow would have given 750 kohms, which is obviously too high), thus
introducing the missing red element.
Or perhaps it's just a historical accident, based on early designs of
coaxial cables in different countries. In Germany, 60 ohms was used.