Question re feldgrau vs. silver em buckles

[Michigan Dawg]

Can someone tell me what year em belt buckles (either SS or heer) began to appear painted feldgrau? Was there a particular reason for this?

Also, someone once told me that nco ranks were allowed to continue wearing the silver buckle while lower ranks were required to wear the feldgrau version when they appeared? Any truth to this and if so is there a regulation so stating?

Thanks for any information you have to share.