The CMYK color format or color space, builds the colors from a combination of cyan, magenta, yellow and black. While computer screens use the RGB format, CMYK is the standard color model in offset printing.
The values for cyan, magenta, yellow and black are defined in percent, where a higher percentage represents are darker value. Some use values of 0 - 100% and some integers from 0 to 1 to represent a CMYK color.
CMYK is not yet supported in CSS, but it is suggested as a new standard in CSS4. In CSS4 it will be possible to use CMYK colors in the following format
cmyk(C%, M%, Y%, K%);.
background-color:cmyk(100%, 0%, 0%, 0%);
color:cmyk(100%, 0%, 0%, 0%);