To print on non-white paper? But I think then the ordinary cyan, magenta and yellow inks can't be used. Normally those are translucent in order to create red, green and blue via subtractive color mixing. E.g. overlaying yellow and magenta dots creates a red dot.

But if the paper can't be assumed to be white, CMY need to be opaque, otherwise yellow on black paper would just look black. Then you can no longer create red, green and blue. So you need additional red, green and blue pigment, likewise opaque. So "CMYRGBKW". Then the other colors can be mixed via dithering the eight base colors as usual.

Or maybe your printer still needs white paper, and the white pigment has some other use?

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egypturnash 2 days ago | parent [-]

opaque white + translucent CMY would work, assuming you can get a white formulation that doesn’t gum up the print head.

	▲	cubefox a day ago \| parent [-]
		Yes, though that would mean they need to stack three drops for red, green and blue, rather than two as in CMYK. Which might create some quality issues. At least CMYK printers avoid the triple stacking for black which CMY printers would have to do. With CMYRGBKW there would be no dot stacking (subtractive color mixing) required at all, resulting in less required ink. Though needing eight base inks rather than the five in CMYKW might be a larger disadvantage.