So touch ups on playfield need to be enamel and the same brand as what ever paint on or under?
And the apron is just simple Gloss Black Automotive.
I have nearly worked it out 
The apron can be enamel of gloss black automotive, the enamel will get a slightly glossier finish.
Have a look at this for you playfield:
http://aussiepinball.com/index.php?topic=5421.90
