Plastic wrap background

I started this sketch by laying down some colors with the vague idea I would paint flowers.  So I put purple and pink on the top half and greens on the bottom.  Then I covered it with plastic wrap until it dried.  I've been meaning to try this technique for a long time and finally got around to it.  I think I might have used more pigment, it dried very pale.  I decided to practice delphiniums as a warm up for a large painting I am doing.  The background colors muddied my flower painting a bit which I thought was a little (okay greatly)  frustrating.  If I use this background technique again I think I would draw my subject first and mask, and then lay down the background colors.