Transparent colors may need to be mixed with other darks and even black. These dark colors use as a tint with white creates a color closer to white. Travel between these two extremes. Rinsing the brush can be avoided by transforming whatever is on the brush toward a nameable color by adding that color or the color that when mix becomes that color or away from that color by mixing that color’s opposite.
And at the same time be aware if you are going darker or lighter. To go lighter and keep the color add white, to go lighter while changing colors add whichever color is lighter and takes you closer to the desire color. To make a jump between colors, either go lighter or darker by mixing in a color that goes away from the nameable color if you want a bigger jump. Keeping away from just adding white or black makes for more surprising color.