An old friend and master of watercolor taught me decades ago that some of the loveliest, luminous greys come from mixing whatever is dried in your palette's mixing area. I usually have a variety of colors there...I can warm or cool my gray by sweeping my brush into whatever's available, without ever dipping into a pan of color.
More water makes a paler value...less makes a rich, darker grey.
Here's Pepi in the light of my desk lamp, just painted with those same luminous neutrals...next time, instead of washing your palette for a fresh start, try this! No need to waste colors unless you just HAVE to have a clean spot to mix a pure color...
