Xerox 8400 printing b+w with colour consumables

[Anonymous]

Hi

I'm running a cups server from cups 1.1.22 on Scientific Linux 4 and printing from other linux clients.

Our Xerox 8400 color printer (using the Xerox supplied ppd file) is using colour consumables to print most black and white files instead of the
black ink consumable.

What I'd like to happen is for colour postscript files to print in colour and black and white postscript files to print using the black ink only without the user having to specify whether to print in black and white or colour.

I notice that printing plain text files does seem to use only black ink, so the problem seems to be particular to postscript documents.

Can anyone suggest how to obtain the desired behaviour for black and white postscript files.

Thanks

Roderick Johnstone