Karel Appel studied at the Rijksmuseum school, that sanctuary for the great paintings of the golden era. He was a prodigy. So where did this come from? You might think you would find it at the Stedlijk, the modern museum, which has many 20th century modern masters. But no. This was at the Rijksmuseum! I and one other person went to view it the morning I was there. Everybody else was viewing Steen, Rembradt, Vermeer, etc.
Appel was also a long time favorite of the Stedelijk Museum. In fact, there is an Appel room, which is entire painted, walls and ceiling, by Appel. Here is a small piece of a larger painting that was on display at the Stedelijk: