I use this technique, but I don't purposely pick any one color. Instead, I take my palette scrapings from the last painting session -- if they are still fresh enough -- and blend them thoroughly. I get some nice greys this way. I can always "push" it into whatever color family I need. I usually don't use it for all my mixtures, though, since sometimes I do want some colors with high chroma.
"Yellow House, Snowfall"5x7, oil, en plein air
Not for this scene, though. The air was filled with falling snow and an even light. Greys abounded. The scene was almost monochromatic. What a perfect way to use up yesterday's paint!
The day before, my scrapings yielded a big pile of a mid-value, pinkish grey. I was able to push it light enough for snow, and to add Cadmium Yellow Light to get the color of the buildings. (I added a tad of Phthalo Blue to dull it down a bit for the shadowed parts of the house and the potting shed.) Even the patches of weeds and the dark silhouettes of the young sugar maples started off with this "mother color."
