Thanks @LarryBradford ! I knew I was missing something. This company's server crashed on Wednesday and we restored a copy of MAS90 to a local computer while they were working on the server yesterday. Today, they will be working from a Wednesday backup on the server and need this workstation just as a reference to re-enter transactions. (Yes, we tried copying it back to the server but it's on a BDR so it would take 17 hours. Customer just wants to start working again.) I need to make the background color obvious that this workstation should not be used to enter live transactions any more.
TLDR; figuring out how to change the background color was not something I wanted to waste time on. Thanks again, Larry!