CMYK is a suggested standard for CSS4.
CMYK colors is a combination of CYAN, MAGENTA, YELLOW , and BLACK.
Computer screens display colors using RGB color values. Printers often presents colors using CMYK color values.
CMYK is not supported in HTML, but it is suggested as a new standard in CSS4.
While waiting for CSS4, you can include W3Schools' Color library, and use CMYK as an HTML attribute like this:
Try it Yourself
<p>London is the capital city of England.
It is the most populous city in the United Kingdom,
with a metropolitan area of over 13 million inhabitants.</p>
W3Schools Color Library