Fresh air door color question

[blue440duster]

Looking for some advise on the CORRECT paint to use on the fresh air box/heater box doors.

Not sure if that would be matte black, flat black....semi-gloss...or?.....

 

[gregpurcell]

I sell a lot of them on Ebay. I'm not certain if it's "correct" but I hit them with flat black and then a semi-gloss clear coat. It gives them a good "not to shiny, not too flat" look.