Digital BW, The Print

>I am using a Canon S750

I can only speak for my Epson printer, but maybe this will help...The
Epson slowly uses the color inks even during BO printing, but only
during the cleaning cycles, not on the print.  

If the Cannon is using the colors on the print then you should be able
to see color dots with a loupe.  That would be the first thing to
check.  If there are color dots then either a setting is wrong or that
printer can't do true BO.

Regards,
Clayton


Info on black and white digital printing at    
http://www.cjcom.net/digiprnarts.htm