I could use the extend='min' kwarg in the colorbar call to extend the colorbar downwards.

I would like to modify the color of this triangle at the bottom of color bar. To make it, let's say, yellow, I tried the above code with tab20c = cm.get_cmap('tab20c', 256).with_extremes(under='yellow'), but the triangle remains blue. I have read about .with_extremes()