Now the palette knife - its main quality is scraping, having new color intrude on the old but not kill it, rather let it peak out in just the right proportions. That's why everyone is so into Gerhard Richter's work with scratched out surfaces. It marries the old and the new in unexpected combinations - the flavors of ice cream never before attempted together.
You see the function of color best in Monet, Rothko, Pollock, Kandinsky. De Kooning I think was a total anti-colorist just as Picasso before him. Vuillard and Bonnard, Matisse - the fauves are seeing color in a completely separate light.