I was experimenting with using pastel as an underpainting and thought I would post the process and result here.  I was doing a small painting of a green and yellow pear and a red apple.  I wanted a color that would be both somewhat complimentary and harmonious.  I chose orange as it worked well with the yellow and red of the pear and apple and was one away from being a direct compliment to the green pear  After doing a quick drawing and massing in of dark tones in an orange pastel I took a brush and washed it all down with rubbing alchohol moving the wet pastel in to areas that were lighter.  

Next, I massed in the dark allowing some of the orange to poke through

Then I put in the rest of the 3 major tones using local colors and keeping it flat and simple.

At this point I'm wondering why I uses an "undercolor" because I felt like it had disappeared, but I thought why not just finish and see what happens so here is the next stage

The final stage has the lightest lights and darkest darks and I do see some of the orange peaking through especially on the background color.  I will probably do more of these to see what works color-wise and what doesn't.   The pros of this is that it's a very fast way to tone a canvas and see what the abstract shapes look like.