Change the appearance of CMYK black (Illustrator, InDesign)

Pure CMYK black (K=100) appears jet black (or rich black) when viewed on-screen, printed to a non-PostScript desktop printer, or exported to an RGB file format. If you prefer to see the difference between pure black and rich black as it will appear when printed on a commercial press, you can change the Appearance Of Black preferences. These preferences do not change the color values in a document.

1. Choose Edit > Preferences > Appearance Of Black (Windows) or application name > Preferences > Appearance Of Black (Mac OS).
2. Choose an option for On Screen:

   Option	Description
   Display All Blacks Accurately	Displays pure CMYK black as dark gray. This setting allows you to see the difference between pure black and rich black.
   Display All Blacks As Rich Black	Displays pure CMYK black as jet black (RGB=000). This setting makes pure black and rich black appear the same on-screen.

3. Choose an option for Printing/Exporting:

   Option	Description
   Output All Blacks Accurately	When printing to a non-PostScript desktop printer or exporting to an RGB file format, outputs pure CMYK black as using the color numbers in the document. This setting allows you to see the difference between pure black and rich black.
   Output All Blacks As Rich Black	When printing to a non-PostScript desktop printer or exporting to an RGB file format, outputs pure CMYK black as jet black (RGB=000). This setting makes pure black and rich black appear the same.

Source: Adobe