Here are three coloured twenty minute life drawing poses on tan paper with construction lines drawn in conte crayon and the figure painted in white, black, burnt sienna and cobalt blue.
In addition, the two, five and ten minute drawings on black paper were drawn freehand in just white and black gouache, following on from this picture I admired last week in the Manchester Art Gallery.
I switched between different sketches, either using a large flat brush filling space or a soft squirrel mop that comes to a point and tends to free flowing lines.
kestrelart 
That fist quick study on the black paper is my favourite. I really respond to the spontaneity in all of them.
Thanks
I was amazed how those quick sketches turned out. I think switching from flat brush to a more expressive mop and starting monochrome is a technique to explore further.