Okay.
Firstly reinstall, so you have all files restarted.
I suppose you want to change the colors? What you do is this:
1:
Open Document Explorer: Go to your San Andreas directory. ( C:\Program Files\Rockstar Games\GTA San Andreas\ )
2:
Go to \data. Click on Vehicle.dat ( Or so )
3:
It should have the colors at the top, search for a vehicle and then change the colors. ( Don't use the ones with warnings )
4:
Save and exit, boot up the game.
I think it is based on those lines, I didn't play/mod San Andreas for years.