Karin,
My understanding of tonalist painting is that you paint your work from a value perspective, which is what I do. So I believe that most work of this type is created by first painting a monochromatic undertone and then glazing and painting color opaquely. The thing about this type of painting is that you match the values of your color to the values of your undertones. This means that if you put down a value 7 undertone in a cheek, you put a value 7 flesh tone over it. The tonal undertone becomes a bit like a roadmap.
You have done the same thing when you created your grisaille paintings - you would just need to take it to the next step and bring it into color.
They did amazing things when they got the value structure correct!
