In 2013, I was given some Daniel Smith watercolour paint to test out by a friend. I've already used up some of the tubes but there are three tubes that have lasted me for more than five years. Those three colours are Quinacridone Red (PV19), Quinacridrone Magenta (PR202) and Phthalo Blue (PB15:3).
It's really quite difficult use up these colours for several reasons.
Quinacridone and Phthalo colours are have incredibly high tinting strength. Only a tiny bit of paint is needed to create an intense wash.
The other reason is, there aren't many subjects that require using large amount of red to paint. Red doesn't appear as much compared to other colours, like blue (sky) or greens (plants). I usually use red to neutralise the greens, but you don't need to use much.
Phthalo Blue is a colour that I like, but I'm very cautious of using it because of its tinting strength. When it comes to painting the sky, I prefer to use French Ultramarine because I like the granulation.
These are the typical mixes you can get with the three colours.
I kinda like the mix of Phthalo Green with Quinacridone Magenta to produce a really dark colour that's close to black. It's green for painting greens that are in dark shadows.
So I still have a long way to go before using up these three colours. Maybe I should just throw in a yellow and paint exclusively with this limited palette. That way I can use them up fast and explore other colours.