V 3.0: Lens flares & dirt, visor reflections / water droplets, god rays, depth of field, night & thermal vision scopes, dynamic wet surfaces with reflections, rainbows, volumetric light & fog, colored speculars and many other effects.
in-game screenshot showing the "dynamic rainbows" feature where both intensity and shape of the rendered rainbow are dynamically calculated by various environment factors.
See also Moddb.com
'A feeling of hope, stalker. Hope in the distance, a feeling of safety, joy ... Bullets shred trough armored vests, skin and even soul, but hope ... hope dies last.'
The dawg who saw the rainbow (pun intended).
Just what the zone missed.