To make sure that two different intersections that should be stitched with the same thread get the same color of paint, it is necessary to mix a fair amount of each color. I store the paint in small paint cups. Because I sometimes run out of a color on a larger canvas, or want to do a design again, I keep track of the recipes I use for each color. This also helps when I need similar colors for a different design.
The paint used on most hand painted canvasses is acrylic. I mix with glazing medium to get a freer-flowing paint, as well as water to get the right consistency. I find that I like the paint to be a little runny without being watery.
Often I will mix a strip of related colors. For example, the strip shown starts, at the left, with the Cadmium Yellow Deep Hue straight, and each cup mixes in more and more white until the rightmost is a very pastel yellow.