Sorry can't add more on paint code numbers for specific colours but the following about the paint process may be of interest.
The first coating is applied in the steel rolling mill. Normally a zinc containing coating. This gives rise to claims about "galvanised" bodies. Not really true but good for marketing. This gives a slightly rough surfaceas well as providing basic rust protection.
In the car plant a dip paint is applied ( electrophoretic, if interested). This coats the inside as well as the outside of the panels and provides additional rust protection, including cut edges and welded areas. This is baked at high temperature. This is a single colour, a shade of grey, but does not have good UV stability so must be protected on external panels.
Next primer surfacer is spray applied. This provides the base colour, some chip protection and UV protection for the underlying coat. This is the paint colour you normally see in the engine bay. Depending on the paint system used it may be baked but more modern systems are force dried rather than baked.
Next comes the final colour, known as basecoat, this has the metallic effect and colour. Finally clearcoat is applied and baked to give the shine we all look for but also provides protection against acid rain, scuff mark, petrol, bird poop etc as well as adding some more UV protection.
Some car makers apply basecoat under the bonnet a few also apply clearcoat to certail areas. Most save money and keep the primer colour.