I finally had some time to work on gamut masking. The principle is simple: take a color wheel (In my case a printed out YURMBY wheel), cut a shape our of a piece of paper, and overlay it on the wheel. The visible area is what is called a Color Gamut, containing all of the possible colors you can mix within the shape.
The most common shape is a triangle, which makes it easy to get a decent variety and have a good amount of color choices within the range.

The technique for Gamut Masking is well explained in various posts by James Gurney (I believe he kind of invented this method):
Gamut Masking at Gurney Journey

After masking out a triangle, the goal is mixing the colors you have at each vertex, called Subjective Primaries. Additionally, Subjective Secondaries (that is, colors found on each side’s midpoint) can be mixed, to further save time when painting.

Premixing is really time consuming, at least for me, being a rookie. Still, it does save a huge amount of time when painting later on. Here are my attempts:

Warm Gamut

 

This was my first mask, pale pinks and greens, strong yellows. I actually grabbed this from Richard Robinson’s Interactive Gamut Mask Tool. But I mirrored it horizontally when printing out, as I prefer having warm colors on the right hand side.

I then matched the color at each end. Starting from the top left, the third yellow, the fourth pink, the third green. Then, I expanded these into 5 different values to make Color Strings. I skipped the secondaries, and painted the next swatch.

 

Lastly, I applied it to my test landscape.

 

Not having any blue, I had to rely on grays to keep balance in the scheme. I am quite happy with the result, although it looks a bit muddy. Pinky shadows help green look greener (which might as well look too starking in the context, and might have been looking better if a good deal duller)

Cool Gamut

I then swapped the triangle the opposite way, and using the same complementary pink/green, I basically replaced yellow with blue. Kind of challenging.

 

I ended up with my blue (ultramarine plus white only) being way too washed out/ Blue having the top chroma at its lowest value, I used the out-of-the tube one for my darkest tone, and killed saturation by adding white.

 

The resulting swatch sees blue being way inside the wheel, more than I really wanted, but I guess it’s no use with blues on higher values.

Painting a landscape is far more complex without yellow, than without green. This type of gamut gives a very cold look to the picture, making it look like a frozen, lifeless landscape.
Here is a final comparison between the two

 

 

Ths kind of landscape might in any case not be ideal for testing out gamuts, as it lacks enough hue variety in the high chroma range.