I’d mix the colors in Quark XPress or I’d create DCS files in Photoshop.
Sadly, I do.
Color Key proofs made from the actual negatives used to burn the printing plates.
I remember them vividly as a regular part of my day-to-day existence some, um, 30 years ago.
I still get hard proofs like that, though they are merely just to see separations, plate making is still digital. 
I’ve no idea how this would work.
@silence04 it really bugs me that I know your avatar from somewhere but I can’t remember where from.
I’ve been scratching my head. There’s something closely associated with it. Then it hit me … grease pencil!
I had a vendor using these all the way up to 2000.
It was the only way to get color proofs of 4-color photos going on fired ceramic porcelain panels.
They’ve since moved on to a heavily profiled proof printer.
Registration marks. Line em up and stack em up on a piece of white paper.
Color keys, Matchprints, and duotones, oh my!
oh yeah! what about non-repo blue!
haha its from an Alex Grey painting, he does a lot of album artwork for the band TOOL 
Oh god DCS files.
Don’t know the band or the artist though, it will remain a mystery 
non-repro. 
