The process separates various elements, which is not dissimilar to a lithography technique, in this instance 1. the bulk 2. the shading, and 3. the texture.
I usually (!in fact always!) work in black and white. I'm only showing the black and white scans here, you can see the colours in the final image.
I prefer this technique because of the ability to fine tune the colour throughout my images, and it also allows some room for experimentation, on those days when I feel fancy-free.
Each element is scanned in and coloured first using the ‘duotone’ feature; once it’s coloured I then tend to adjust the hue/saturation and check the ‘colorize’ box, so I can edit each layer live in the document.
The layers have various ‘blending modes’ added to them (mostly multiply, but by no means just multiply, depending on the tone/colour).
Here’s the effect…