I’ve always wondered how games generate an IR vision or night vision anybody have any idea of how they do this?
While i am no expert, i would imagine that each material would have an “heat” attribute, and thus rendering would be a function of attenuation of that heat attribute with distance and then converting that value into a gray scale (or green 
) render.
As a guess; for IR you could supply a simple heat texture for every model which you switch too when IR is turned on. Or set some heat statistics and have them rendered with the appropriate heat colour set but with no texture.
For night vision you could set the colour to green and then up the lights. Then add a bunch of overlay effects directly infront of the camera for dust and static.
Another way to do it would be just to use an alpha map texture for every model, then just color it appropriately. The level of transparency in the map can determine how red or green something is.
yeah one quick way would be. just use green texture maps (or grayscale with material coloring on, probably better if you want to include i-red vision)
so when in night vision, use grayscale texture maps, and also maybe use openGL FOG.
thats probably the easiest way of doing it without shaders.
Other things to consider is specular. but really you would need to play around with it, and tweek it unil you are happy with the visuals.
Thanks guys!!!