Those engine exhausts are GORGEOUS! What color marker are you using to clean up the edges?
Those oval-shaped details could not have been easy to cut out!
Actually, I use watercolour paints and mix my own colours to match (as closely as possible) to the colours I need and then I use a "dry brush" technique to paint the edges.
As for the oval cut-outs, you will need a very sharp knife with a very fine point (and take your time with it).