friendly knuckle cracking I wouldn't normally do this, but I did say I'd die on this hill. I'm a tenured professor of art at a major research university. Firstly, maybe I shouldn't have said "saturated," but then again, you wouldn't argue that your earth tones, for example Yellow Ochre or Burnt Sienna aren't saturated in color?

I have a particular expertise in historical scenic painting, (granted, largely for theatrical and ceremonial practice, but that's where we have the oldest examples of painting a fake thing to look real, see trompe l'oeil https://www.britannica.com/art/trompe-loeil )

In these examples, it's clear that the painters started with relatively saturated midtones, and used washes to take the shadows down and clay filled light colors (think gouache) for the highlights: https://masonicheritagecenter.org/backdrops-gallery/

As to the expense of saturated colors, it's the scholars claiming saturated colors, so the expense was made, obviously. But was yellow the final color, when it is the perfect base coat for a two part skin tone using first yellow, and then pink? In the first image in the article, you can see that half of the face is yellow, but that the other half is light colored skin. This exact theatrical layering practice has been used, first yellow, and then pink.

The fourth and eighth images in the article looks extremely similar to the scenic backdrops I've linked above, but one is from the same time period as these statues, and the other is from hundreds of years later. There is a clear similarity in the final work. I believe it's obvious that both painters used dry pigment mixed down to a thin consistency, and used a series of 5 to 7 quick layers to achieve fast, one session results.

This practice doesn't have anything to do with what we call oil painting today, which can be quite laborious and is normally achieved over multiple sessions. These artists would have wanted to knock out a work and get down off the ladder.

Happy to discuss further, all the best.