If black in CMYK is C=75 M=68 Y=67 K=90 and not C=0 M=0 Y=0 K=100 then what is 100% white C=0 M=0 Y=0 K=0?

Question

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Why can't we get 100% black by clicking on the black icon and have to put it in manually, while getting white this way is no problem?

Answer 1

CMYK builds on the absorption palette. The value specifies how much printer ink of that color will be transferred to the paper. The implication is that the print is on white paper, so yes, white will match all zeros (no ink will be transferred to the paper at that point).
If you turn K to the maximum, the printer will put a dot in this place with black ink, and it will be really black. But it won't be the blackest you can achieve with your printer, because it has three more ink colors that can also be transferred to paper. Their use is optional, but adding these colors in the specified amount will "strengthen" the black by taking even more of the light falling on the paper.