my Tamiya M1A2 is nearly ready for some weathering but before that i just made a final thought about details and variations. One of these where the exhaust grilles which i see sometimes painted in (worn, roasted and sooted) US desert or kinda flat black. Latter is a heat resistent paint like it's used for ovens, exhausts etc. i guess?

(Picture gratefully taken from PrimePortal)
Any standards/regulations for painting this part on the real thing?