It would present a problem if i had just done the white as white because it would stand out like a sore thumb. What im doing here is matching colour and tone - you can apply any colour you want to the PF but if the tone is wrong then it glares at you and leaps out to the eye.

If i was using standard colours then everything would be mixed with a touch of yellow ochre... if you are matching existing paints on a PF then yellow ochre is your best friend... you will not match unless you add this to the pallette, sometimes you only need a tiny amount - it just takes the glare off the new paint.
 remember these PF's had a linseed finish put on them which yellows over time - you cannot get this finish off without removing most if not all the artwork. So unless you are completely repainting it ( massive amount of work) you need to fake the yellowing and yellow ochre is the go.
With Pantone inks this is achieved with yellow and a tiny touch of standard red.

Remember - there is no such colour as white on any pinball, itll either be a very pale yellow/orange or pale blue etc