No Color
I came upon this post about value and the benefit of painting with very little or no color.
When I try to explain what value is, it usually goes something like, "Imagine if you could see in black and white." Value is - or are - the gray components of a tone. Color gets the credit while value does the work.
With that in mind, I dashed off a quick study using only a handful of tones. This is ivory black, warm white and a pinch of cad yellow deep. I've also posted the setup.