[NTG-context] Can ConTeXt output in grayscale?

I have a document with lots of color text, Metapost art, and various images in PDF, JPG, and PNG format. I might have the printer just print in black and white, as it cuts printing costs in half. Is there a way to tell ConTeXt to compile everything so it appears grayscale, so I can better visualize how it would look printed? --Joel