I was looking for a way to improve the tyre smoke look (..which I feel needs some serious attention), and found at least some settings to give it a more natural color than the default one. I think it was Cereberus that posted these somewhere. You'll need to simply edit your tyre_smoke.ini, which can be found under /STEAM\steamapps\common\assettocorsa\system\cfg.
I should post some comparison screens maybe.. Soon 
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Code:
COLOR_BASE=0.6,0.7,1
COLOR_RANDOM=0.1,0.1,0.1