The title is pretty self-explanatory. In the Republic Commando video game and the two or three episodes of The Clone Wars in which Clone Commandos appear, why do their helmet T-visors glow? I don't recall it ever being explained in the game or in the books or in the Expanded Universe in general, and I've reread them over and over. Is it part of the armor's shield system? A night-vision aid? Part of that visor-cleaning system? Or is it just to look cool?
While the Rule of Cool almost certainly plays a role in it, the objective is probably to give the viewer a visual indicator that this armor is more high-tech then normal Clone armor.
The helmet of the Katarn-class armor had a HUD or heads up display that consistently displayed tactical data such as the location and distance to the target, the health of the wearer and the strength of the suit's shielding. The helmet could system link to others through the use of an internal communications antennae allowing each member of a squad to keep track of their comrade's health and location. Specialized internal sensors could detect the make, model, and relative accuracy of every weapon that a commando used, and could adjust the format of the targeting reticule for differing weapons. The Helmet had a built-in filtration system which could extract oxygen from toxic environments. The visor was designed to incorporate electro binoculars and night-vision modes.
Katarn-class commando armor | Wookiepedia