CMYK mode refers to dot size of printing C, M, Y, K when reproduce colors, therefore, the range of values C, M, Y, K is from 0% to 100%. C0% M0% Y0% K0% represents white, C100% M100% Y100% K100% represents black.

Theoretically in sublimation ink, different proportion of the yellow ink, magenta ink, cyan ink can be achieved for all color. 100% of the yellow, 100% magenta and 100% blue mixed together, can produce black.

However, Since the ink used in printing is not ideal ink, actually used yellow ink is not the case, this part of the reflector 500 ~ 700nm is insufficient, at 400 ~ 500nm absorption is inadequate. The reason for this is that yellow ink presented a small amount of magenta and cyan components. Other inks may also have the same problem. In printing or printout, if we do not use black ink, mix 100% of the yellow, 100% magenta and 100% blue will give a brown. We usually add a black to guarantee that dark and gray are not color cast. So to add a black version to show true black.