Plein air Painting makes you analysis your surroundings to pick out what you like and put it in your paintings.
Sometimes it's Just the shape of the estuary or the edge of a river bank. You can narrow it done to just an area that is creating interest.
I will see a range of shades and think they would be great in a completely different colour.
I use the shapes of the cloud to, for a composition or a suggestion of them but use a different colour combinations.