For years I have used a thin dashed-lines or solid-lines for Xrefs backgrounds. but they're rather 'busy' and can be distracting. I tried DOTTED instead for a "screened 25%" appearance instead. It stands out and is actually more 'snap'-able for new work on-screen, yet it fades into the background more subtly than the DASHED when plotted. It works better if the Xref is one dedicated layer.
You may have to experiment with pen-width and spacing depending on your printer-plotter to get the screened-density you want.
You may have to experiment with pen-width and spacing depending on your printer-plotter to get the screened-density you want.