change the default "grey" car

[oegge2]

well if i do that then all my custom skins would be grey cars ingame :/

but i want the grey cars to be a custom skin

[Demented]

Yes, it reverts the default skin back when you start the game and it updates.
Solution = disconnect your internet before starting the game while working on your project.
I don't play online so I only connect my gaming PC to the internet about two times a year to update things, the rest of the time it's offline and works just fine.