K: black (like on a monochrome print or copy) is always slightly less dark as CMYK, composite or "rich black".
Printers will often introduce varying amounts of cyan and magenta to produce a richer, darker black.
Take a look at pg 8 of the ANSI A 11% color test pattern, which shows various rich blacks, compared to K black & composite black.
=^..^=
Bookmarks