Wikipedia page Colorist has some comic art usage if it helps. ("In comics, a colorist is responsible for adding color to black-and-white line art.") Could we say Use for persons who add color to black and white illustrations (printed or drawn). In relator terms we have Rubricator and Ill. with no scope notes. I wonder about the stencil part of this?

I guess I forgot to add warrant for colorist adding color to stencils. This is not what I found on Monday but it'll do.

http://www.artbma.org/paintedprints/html/PP03.html
This woodcut is an example of a sophisticated stenciling technique. The colorist applied a wide array of paints through a series of precisely cut stencils. Even the areas of shading were painted on through stencils. The colorist then added gold and silver highlights to the comet and stars by hand. These efforts suggest that this beautifully painted broadsheet functioned as deluxe wall decoration.

I did more checking and found something more general on www.answers.com. There a colorist is defined as:
a painter able to achieve special effects with color

I like this definition because it forgoes having to spell out the medium. So, how about ?

Use for person who achieves special effects through applying color.

Rubricator is a RT. And the RT should be Ill., not spelled-out "Illustrator"

I like Bruce's first SN. Adding color is not necessarily a special effect and perhaps the line-art is printed in red on brown paper (just a thought). I think we should keep it simple:

Use for a person who applies color to drawings, illustrations, or photographs.

This way, it doesn't matter if the colorist is applying color by hand (paint) or by stencil (pochoir), or whether it's a wood cut, a comic strip, a photograph, or a drawing; they are just adding color to a monochrome image.

Also warrant for the word as in the OED definition - a person who is a master of color: (as in:
Donald Judd, colorist ; The Colorist: Designed to Correct the Commonly Held Theory that Red, Yellow, and Blue are the Primary Colors, and to Supply the Much Needed Easy Method of Determining Color Harmony; Together with a System of Color Nomenclature and Other Practical Information for Artists and Workers Or Designers ... (1925)) Is it okay to choose a meaning based on warrant rather than definition?
Are we okay with using warrant based on the one v. the dictionary definition (master)?

There are definitely two meanings of "colorist" out there in the art world: one is a trade -- the colorer who colors uncolored outlines (the sense John is looking for); the other is an epithet -- a painter who perceives/represents things more in terms of color than in terms of lines, or a painter who is skilled at color theory.

I was hoping I could find something in an early modern Book of Trades in English, but no luck yet.