Personally I use pre-tubed neutral grays for situations like these mountains.
No problem if you don’t have them; for low-saturation colors like these, I would start with a 2 or 3/1 black/umber mix for darks; mix in white until the correct tonality is achieved.

From there, you can add small amounts of color (black/yellow makes a green that would work all over this picture) to your neutral gray piles, and you can ‘warm them up’ with cad yellow or umber, and ‘cool them off’ with white or a little blue.

Tell your teacher that gray on the palette is not a crime:). I have 4 piles of neutral grays on my palette every day.

A common way to desaturate is to first, mix the color you want using white, and the one or two other colors it takes to achieve the “pew” you want to be in. Next, having premixed a string of neutral grays, start adding the neutral of the same value as your first mix until you achieve the grayed down color/value your want.

Neutral grays can be mixed using ivory black, white and a smidge of yellow ocher or raw umber. The ratio is about one black, about one-quarter raw umber and white in steps to make a string of grays. Some artists mix strings of 9 grays, others mix 5, and some mix a string of three.

Mixing neutrals this way is a bit of a feel as your go thing. It also depends on whether you’re using yellow ocher (and which brand), raw umber, or burnt umber, as some artists use.

If you’d like to buy a black that comes very close to making neutral grays, get a tube of Williamsburg Italian Black Roman Earth to use with white to produce neutrals.

I could add actual grey, but my teacher will find that blasfemous

:confused: why?

By all means, add an actual grey! It is a very grey reference.

Double…..sorry

Indeed, “distance” is often given a blue cast, but not fully a saturated blue. Generally, it’s a grayed version of blue, which can be achieved by using some thing that won’t materially alter the “blue cast.” A grayed blue (often a glaze) works well.

Take a look at 22:12, not exactly the issue we see above, but he is actually scumbling.

Color-correcting a photograph is off-topic for this thread. This thread is about is about paint mixing, not photo-manipulation.
Please stay on-topic.

Thanks.

@stapeliad: I appreciate that photo-manipulation is not the topic, but the OP did ask about desaturated colors, and responders already wondered about a missing blue cast. The reason I placed a color-corrected image, which you removed, was to provide better targets for the mixing.