I just started using a good quality manganese blue again after a 4 year break. I remember finding it essential when traveling but of less use here in Italy. This summer however, there have been a couple of times when I’ve really struggled to get the exact hue I needed. Using the manganese for the last two weeks has made mixing some colors so much easier. I see more colors just by having the capability to get them. ‘Like scales falling from your eyes’ as Gammell said.
The same thing happens every year with my landscape students who bring brand-name yellow ochres outside and fight the chalky color for hours. Its impossible to key your colors correctly with tube paints which are full of extenders which dull the color.
Matching color in nature is hard enough with the right tools, with poor quality paints it becomes almost impossible.