I have actually grilled bacon on a hot can. I have a first gen M42K that I use for magdumps in machinegun shoots and it still works well, It also stayed gray.. The Model 8 is the one that turned different colors.
I work for NIC Industries our product Cerakote is designed to address the issues you are having with your M4-2K suppressor. Cerakote Coating is capable of withstanding extreme high temperatures (Over 1200 Degrees in third party testing) without any discoloration as well as many other benefits to using Cerakote.
If you are interested please PM me to learn more and I would be happy to answer any of your questions