I'm back from a week's vacation with ample leisure (and fine weather) for outdoor painting.  Here is one small result.

One very warm afternoon  I was relaxing on the lakeshore.   Looking overhead, I noticed that the tone of the center of the clouds was equal to the tone of the gauzy blue sky, so that the clouds seemed defined only by their highlights. 

This  cloud study took about fifteen minutes.  I didn't quite succeed in capturing the effect of the light, but there's nothing like painting from nature to capture a moment and to sharpen one's observation.