On new cars when they go through the production line, generally when the air gun used to assembly the bolts gets to the required torque settings it also sprays a bit of paint, so when then during final checks when it leaves the assembly line the quality assurance person ticks of the components which are marked with the paint and don't they dont have to manually check the bolt torque.
Some older cars would also have a dap of paint on selected components bolts to indicate it had been torqued correctly, but this was done manually by the assembler.
On older vehicles paint codes where used to designate which component was required for a specific model, ie on for a V8 Falcon the correct V8 Falcon had a different paint stripe to say a six cylinder Falcon and station wagons would have a different paint strip. That way when Lewegy was assembling the car he only was given a build sheet with the required colourd components specific to that spec vehicle.
Some people when restoring a concourse vehicle will also replicate these paint strips for the specific components to make it look like it just rolled of the production line.
Regarding Capri's the only paint marks I can verify are the red dabs of paint near the gearbox crossmember bolts.