Reticles should be stored at the same temperature as the reticle stage in the stepper or scanner, otherwise overlay errors may occur due to dimensional changes after alignment. Some litho tools allow reticles to be stored inside them for some time before use to allow temperature stabilisation. Humidity levels should be moderate - typically 50% RH is fine. There should be NO static charge in a reticle storage environment. Ionizers are virtually compulsory. However, don't be tempted to GROUND the reticle itself as it will be more likely to be damaged if it is grounded. One cannot discharge a reticle safely by grounding it - and if there is a field around a grounded reticle the field will be focused onto the reticle - so the best solution is to keep the reticle away from ground and to keep it in an ionized atmosphere.

All of the major scope in Black Ops 2 have their own Reticle Challenges. In order to change reticle colors, you'll need to finish all of the Reticle Challenges.

You can access the Challenges in the Barracks menu.

Crosshair or reticle.

This is an opinion based question but may say that the Reflex sight is the best reticle on the game "Call of Duty : Black Ops"

With a holographic sight, the reticle is always on the spot on the target where the weapon is pointed. When a gun is moved left or right, the reticle moves as well, but is still on the point of aim.