Some of the SCR-274-N receiver sets I'm working with have silver colored screws in some exterior places & darker colored (almost black?) screws in other exterior locations. Recently noted was silver screws securing most of the cover & the bottom plate but darker ones near the front panel rim. I expect blackened screws on black painted ARC-5 series sets but I'm curious about their use on unpainted SCR-274 sets.

Is this a standard from the original manufacturers? Should I get a batch of blackened screws as well as the plain metal ones?

Thanks!
Wayne
WB4OGM