I can produce black and white maps from raster images, with areas blocked out with a single 'Pantone' colour. Provided I use the 'multiply' blending mode, I can overlay the black and white map layer over the coloured shading layer without affecting the colours of either. But the exported image does not retain the information required for 2-colour (spot) printing (for a book). I think part of my problem lies in the fact that QGIS does not use Pantone colours; I can mimic the required Pantone colour in CMYB or RGB, but the exported image does not have/retain the Pantone information required by the book printer. The image is full colour not 2-colour.