What new approaches to form did the impressionists introduce and how were these trends continued in the work of the post-impressionists?

The new approaches to form that the impressionists introduce were: 
-Color theory (in light and nature)
- added brown or black color
-Object shadowing
- 'en Plein air' (painting outside)

as for the post-impressionist, they still adopted these techniques, but they add more emotion and personal insight into their artwork.

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