[Lux]

Not all particles can be changed the particle has to support custom colours, the only particle i know of is the boomer vomit particle that uses material prop to change the colour on screen, i don't know of any other particle in l4d that supports that.

You can use particle lights to change the colour of smoke according to the FGD

https://developer.valvesoftware.com/wiki/Env_smokestack
https://developer.valvesoftware.com/..._particlelight

maybe helpful.