I have a document which has color on about 25% of its pages. When I print it in the copy shop, the printer's technically supposed to recognize the b/w pages. However, all pages are registered as colored, i.e. the pages are color-enabled pages which happen to not have any colors on them (but I'm paying for the color-enabled-ness). Regrettably, the staff have to charge me for color because the printer's leased and they have to pay for color pages, so showing them that there's no color doesn't help me.
What are possible sources for b/w pages showing up like that?