On Wed, Nov 21, 2018 at 3:02 PM Jan U. Hasecke <juh+ntg-context@mailbox.org> wrote:
Am 19.11.18 um 11:14 schrieb luigi scarso:

> Perhaps this is still useful 
>  https://www.tug.org/TUGboat/tb31-3/tb99scarso.pdf

Thanks a lot for the hint.

I don't understand the equations but at least I found transicc to
calculate color conversions.

What precision is useful in the wild?

I now use three digits after the decimal point, eg.:

\definecolor [hs-logoblau] [c=0.976, m=0.665, y=0.028, k=0.116]

It's safe to specify a color as 8bit per channel rgb, or in percent. i.e. see for example 

16bit per channel rgb are also possible, but old RIP can have problems 
shows rgb 8bit per channel  and CMYK 0 to 100)

Btw: be careful of the  checker shadow illusion
colors not always look as they are expressed  in numeric form.