File mode: CMYK CMYK working profile: Fogra 39 Grayscale working profile: Dot gain 15%

Any region with pure black (0 0 0 100), if I turn off the cyan, magenta and yellow channels, it gets slightly darker, almost to rich black. Why is this?

  • You do realize you can't actually see CMYK colors on a monitor, right? Some algorithm is pretending to show you CMYK, and giving you the false impression that 100% K is darker than 100% K with other channels -- which contain no values anyway -- are turned off. Doesn't that tell you something about the "simulation" quality?
    – user8356
    Sep 9, 2019 at 18:48

1 Answer 1


When Photoshop shows you a single channel, it does so in a greyscale, rather than the actual colour. This greyscale is mapped to RGB greys, and thus 100% black is displayed as #000000. Which is a darker colour than CMYK 0/0/0/100, especially if you've set Photoshop to display CMYK blacks accurately.

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