Bug 1693395 - Add XROutputColor:PrintAsGrayscale to the grayscale values for CUPS. r=jfkthame

See bug 1676191 comment 32.

Differential Revision: https://phabricator.services.mozilla.com/D105513

widget/nsPrinterCUPS.h

@@ -141,6 +141,7 @@ class nsPrinterCUPS final : public nsPrinterBase {
       macro_("PrintoutMode", "Normal.Gray")       /* Foomatic */ \
       macro_("ProcessColorModel", "Mono")         /* Samsung */  \
       macro_("ARCMode", "CMBW")                   /* Sharp */    \
-      macro_("XRXColor", "BW")                /* Xerox */
+      macro_("XRXColor", "BW")                    /* Xerox */    \
+      macro_("XROutputColor", "PrintAsGrayscale") /* Xerox, bug 1676191#c32 */
 
 #endif /* nsPrinterCUPS_h___ */