Richmond Lewis / Mike Mignola / P. Craig Russell: Ironwolf endpage (p. 96) (hand-painted), detail

In this original color-page (heavy stock paper, with the inks printed upon in blueline) it looks as if most of the background got spray-painted (watercolors), with using various stencil shapes or sheets placed for painting only certain area's further, but leaving other bits as finished already.
Neatly following the inks (by P. Craig Russell, over Mike Mignola's pencils) in multiple layers, with decreasing density consecutively, for achieving a grainy or 'spotty' effect.

As such creating less or more painted-upon bits - totally up to preference. With also remaining able to be checking how things would look with inks, by placing the acetate over any dried up paint.
Characters or more individually voluminous shapes look to be filled in more thickly, like by means of using in watercolor paint non-transparently ("gouache"), instead of the more thinly spray-painted layers.

But there's more. The printed "blueline-reference" seems to have been applied directly onto already painted area's! As the archtectural bits or the bullet-holes and cracks, the wolfhead as well as the lettering are clearly visible as put on top or over painted sections.
Weird huh. Both as nifty. An intricate little bit of fact which I would have never guessed without seeing the actual "color blueline" in this here original color "splash-page" (hah!).

[Layout dimensions 14.5" x 9.7" / 37 cm x 24.6 cm]