The first practical night vision devices were developed in
Germany in the mid-1930s. Night vision goggles are usually
green, because people can see more shades of green than other
colors. Because the eye is most sensitive to light wavelengths
nearer green, the display can be a little dimmer, which
conserves battery power.
Photons that hit the lens at the front of night vision goggles
are carrying light of all colors, but when they are converted to
electrons, there is no way to preserve that information.
Effectively, the incoming, colored light is turned into black
and white. It is also easier to look at green screens for long
periods than to look at black and white ones. That is also why
early computer screens were mostly green.