Printer refused to print until I'd changed the cyan toner - even though I specifically requested a monochrome print.
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@confusedbunny A lot of printers lie about printing in monochrome mode and use the color inks (usually yellow but sometimes cyan) to print microscopic dots in the margins as an identifier. https://en.wikipedia.org/wiki/Printer_tracking_dots
@wildweasel I forgot about that - I've read it before. Maybe that why.