As it currently stands, both the Insurgent and Security forces use the same gas mask which does put a visual effect on how a person looks. I think it can and should be further improved to help differentiate the two by making the two use different gas masks.
The Security forces could use something like the Type M-59 Iraqi gas mask which has a nice olive drab colour to it that would look nice while being in contrast to the black variant being used right now for both forces.
Img Source: https://www.awm.gov.au/collection/C1036752
These gas masks were found within Iraq during 2003 so it seems like something that would not far off to see in the game's setting.