I hope this isn't too much of a stupid question, but I can't seem to recreate this color in GTA and would appreciate the input of others on this specific color on the LAPD's unmarked Chargers. 

 

Spoiler

https://www.gta5-mods.com/tools/lsc-vehicle-colours-index

 

try to use that, i think the color would be called dark steel or black graphite or something like that...(i am at work and don't remember the name of it) and do it under the metalic variant (not Classic)  and hit it with the white or silver pearlescent paint tone.  hope that helps.