Myst is right.
Anything other than gas (smoke) with damage attached, or some kind of temp crit is just plain-jane smoke.
I did see burn try out some new crit types that would work well here. The one he used against me was "crew deorientated"
I can easily see that being adapted to terror gas. Like make all units caught in smoke have no LoS, and call that "Blinded"
also, im pretty sure we got some ppl with basic enough skinning skills to make smoke look "mustard gas" green.