As an unsupported, inelegant, and prone to break hack!, we've amended one of the standard CSS pages for our HealthShare 2018 installation:

    ZEN_Component__core_3.css

(for Windows, located in <InstallPath>\CSP\broker )

Just added a background colour as follows for our live server:

Doesn't display on every page but does on important pages for us like SQL, lookup tables, configuration pages:

.zendiv {

                background: #FFE0E0;

}