[alfazagato]

I use Rover "steel metallic" paint which does not appear metallic at all when it is on a slightly rough surface. It has a slightly blue tinge to soft grey, it is not a hard German metallic colour. It appears to withstand the temperatures that the engine generates and even after a few years still looks good.
I took a very clean aluminium water pump casting to my local parts shop and matched the hue to a readily available aerosol can. Bought one, thought this is OK, and sometimes I have difficulty in seeing if I have actually painted the part.
I am sure that there are similar colours available to you.
The other good thing is that you can re-touch so that scratches etc can be eliminated.