Using spot-color in LaTeX for print-post-processing

I like to use LaTeX to produce nice looking PDF files for printing. So far that has worked pretty well, but in a recent project I ran into issues, so I want to document the solution here. In some printing jobs, there is post-processing involved e.g. when cutting stickers, when putting gold-foil over certain parts of the design or when embossing. In that case, the files need to follow a certain scheme that this areas can be correctly recognized.

In my use-case, the cut-contour lines of a sheet of stickers needed to be given as a separate colour with a certain name. All solutions that I found, where tailored towards proprietary PDF creators like the Adobe Suite or something in this direction. Even harder, if you search for the german words „Volltonfarbe“ in combination with „Latex“ (or even „LaTeX“), you will end up with results offering to buy latex based paint which is not very helpful. „Volltonfarbe“ in this context translates to „spot-color“ and it is very well possible to use spot colors in a LaTeX document.