Helloo,
A few years back i colour coded the engine covers on my dads passat i was driving at the time.
I did a quick write up for the ukpassats forum at the time which ive copied below.
hope it helps! (ps, it was my 1st attempt at painting ANYTHING lol)
Orignal Engine Bay


Covers Removed and Wiped Down

Mask

Wet Sand Covers using 600grit Wet and Dry Paper

Primered with Halford Plastic Filler Primer to remove imperfections and and scratches

Sand again using 600g Wet and Dry
Apply Base Coat (so less paint is needed to cover yellow) Used Halfords Grey Plastic Primer

Sand again using 1200g Wet and Dry
Paint Using Halfords Colour Matched Paint

Then 2 Coats Of Lacquer and.....



(Airbox cover is still inbase coat as ran out of paint!) Its worth the effort and time, do not rush it otherwise will show in the work completed.