If it was mine I would keep the frame a gloss black,it will make a nice contrast,are you painting the engine case? colour is a very personal thing so what ever makes YOU happy is the colour you should paint it.
I dabble in oil painting and water colours,so I have a pretty good eye for colour,that's what I would do.
FYI in the U.S they spell colour c-o-l-o-r,glad to see you still use the Kings English,I'm an ex pat meself mate,born and raised in the old smoke,I live in Oregon
U.S.A now. I have a cousin lives in Perth,
gd'day mate