Every studio I have worked in accumulated colours faster than it used them. A shelf of forty tubes sounds like freedom. In practice it makes a painting harder, because there is always a tube that is nearly right and reaching for it stops you learning what your palette can actually do.
Six pigments — ultramarine, chrome yellow, rose madder, viridian, raw ochre, titanium white — will make almost every colour that appears in this collection. The greens in the water paintings are viridian pulled toward ochre. The violets in the dusk fields are ultramarine and rose, greyed with a little of the same ochre so they stay in the same world as the grain.
The real benefit is not economy. It is that every colour on the canvas is related to every other one, because they all came out of the same six.