I made Fellout, and I made the FO3 and FNV screenshots the OP linked.
Fallout 3 uses post-processing known as "ImageSpaces", where the basic parameters of the rendered frame are changed. Things like brightness, saturation, contrast, radial blur, blur, etc. In Fellout, I pretty much neutralized them.
It also uses "ImageSpace Modifiers", which modify the imagespace of the scene. A Fatman explosion, for example, uses an imagespace modifier. They give you the effects on drugs wearing off, addictions, damage, head-cripple double vision, etc. These work on any imagespace and Fellout generally left these alone.
They are implemented in pixel shaders (SM2.0 nearly exclusively) and are a development of the very fake HDR system used in Oblivion.
Fallout 4 uses the exact same system. It still has imagespaces. It still has imagespace modifiers and it uses the hell out of them. It's not as blatant as Fallout 3 and everything being green, but it's still there.