Problem
Some Xerox Versalinks (e.g. C7020dn) may output mono when color is requested.
Solution
1) Change to socket printing & PostScript 3 output (follow this article)
2) Under advanced settings select the 'Add std. Xerox XPIF header for Versalink (and others)' PPD fragment from the drop-down.
3) Force the header on for all prints