Grand Assortment of Greens
Using the gray scale (grisaille), mix your basic gray colors. To each color add cadmium yellow and you will have greens in 9 shades.
Divide these greens in half and add french ultramarine blue to one half. You will now have a full range of yellow greens and blue greens.
I buy little plastic container that screw together at the dollar store. I mix my colors and put them in these containers. Since they are clear you can see what color is in there. Works great.
Believe it or not I have found that acrylics stay workable longer than oils.