[NTG-context] color question

[Henning Hraban Ramm]

> Am 24.08.2020 um 01:15 schrieb jbf <roma83537 at gmail.com>:
> 
> I have a very basic question about color use that someone will be able to answer easily. The background to the question is that (i) I am completely new to this scene of commercially[offset] print-ready material as distinct from what is required on screen (ii) I am using Mk IV (iii) I need spot colors set up for cmyk, and for now I need shades between black and white (e.g. light gray) for a simple design feature.
> 
> My question is this: is the use of color keywords sufficient? Or in other words, have predefined color names like lighgray already been defined in, say cmyk terms behind the scenes, or must I instead \definecolor[lightgray][c=10,m=7,y=5,k=0],   (or perhaps \definespotcolor with those dimensions, or do I need both)?

First: Color parts use decimal numbers from 0 to 1.

Even if some color names are predefined, you should define your grays yourself – either as shades of black only or maybe with a bit of cyan. Grays in more (process) colors are unstable and might get a tint (color cast) you don’t want. (Of course you could use other colors than cyan for some tinting, depending on your work.)

E.g. I often \definecolor[deepblack][c=.3,k=1] for black areas; the cyan portion evens out some irregularities in print.
Because I don’t trust ConTeXt’s (or my) color setup, I also \definecolor[cmykblack][k=1] to avoid “RGB black”. (But \setupcolor[cmyk=yes,rgb=no,overprint=yes] should handle that already.)

If you want to use grays as spot colors (e.g. Pantone) you must define them as such – but usually you don’t want (to pay for) more than one spot color. Spot gray makes sense if you have big areas of that color, since 100% spot color looks better than any percent rastered black.

See also:
https://wiki.contextgarden.net/Color
https://wiki.contextgarden.net/Spot_Colors


Hraban (printing engineer)