For XO, the green overlay was not a film, as was used by Atari in Battlezone and other games. It was some type of contouring gel, similar to what Cinematronics used in Star Castle and other games. The overlay was contoured to apply to the face of the CRT.
I believe that that XO was only game Atari used this type of overlay on and, as noted earlier, it was only used on a prototype/test basis and never used as a production part (i.e. whatever the results of the testing, Atari made the decision not to use it after test period ended).