A slight tangent for the interior exercise, as I think it’s supposed to be in black and white (achromatic). I took a bit of time out to play with getting a better tonal range with coloured pencils.Complementary blending seems to work to good effect – though the complementary colour can show through. Either way round works. In fact, on page blending of colour works at least to a degree.
Pencil over or under the colour also seem to work, despite the wax base in the pencils.
Both of those approaches seem to work better than black or grey with colour. White on colour has very little effect – more like a blender than anything else.
Putty rubber on colour is partially successful only. Works best on lightly sketched colour.