Having tried two or three so called car paint matches (bauxite, rail blue & rail grey from memory) without any success, although I did use car paint for BR maroon.....
I use Railmatch rattle cans for all my loco's & stock, the advantage for me is the perfect colour match every time........the only downside to these cans is the dreaded clogging nozzles. I always save the working nozzles from empty cans as spares though clean the nozzles in white spirit after use which helps.
I usually brush paint my diesel cab interiors & use Railmatch Rail Grey (enamel)
Phill