All,
Apple has been using the "print-color-mode" value 'auto-monochrome' for many years to specify that the printer should automatically choose between 'monochrome' and 'process-monochrome' (whichever is the best choice for the current marker and media combination). It was recently brought to my attention that we had never registered this value, so here is out registration template...
Attributes (attribute syntax)
Keyword Attribute Value Reference
----------------------- ---------
print-color-mode (type2 keyword) [PWG5100.13]
auto-monochrome [APPLE20171101]
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Michael Sweet, Senior Printing System Engineer