Put the color on using the "Chalk" brush.
The feature of Chalk is that it will not be mixed with lower colors and fit for covering.

After putting colors suitably, use "Blender" from the "Tinting" of brushes category to blend colors on the screen, then make them natural.
The feature of the "Blender" brush is that it doesn't give colors by itself, but blend colors on the screen.

When people drew with analog painting tools in old times, they used to put paints on canvases and blend by brushes with water, but we can use the same technique now.
The point different from painting of "Digital Watercolor" is that "Blender" is opaque so the more you blend, the more saturation of colors goes down. In addition, since there is no need to make it dry, you can do over again without limit even if you mistake procedures.