Color theory defining the CMY primaries as substances that "absorbed" only one of the retinal primary colors: cyan absorbs only red (−R+G+B), magenta only green (+R−G+B), and yellow only blue violet (+R+G−B). It is important to add that the CMYK, or process, color printing is meant as an economical way of producing a wide range of colors for printing, but is deficient in reproducing certain colors, notably orange and slightly deficient in reproducing purples. A wider range of color can be obtained with the addition of other colors to the printing process, such as in Pantone's Hexachrome printing ink system (six colors),
Blue–green distinction in language different and common words: while ' refers to the color of arterial blood, ' is a red tending towards yellow or the color of clay. Italian distinguishes blue ('), green (') and grey ('). There are also common words for light blue (e.g. the color of the cloudless sky): ' and ', and other for darker shades, e.g. ', indigo. ', the English equivalent of azure, is usually considered a separate basic color rather than a shade of "blu" (similar to the distinction in English between red and pink). Some sources even go to the point of defining "blu" as