One reason that I like gouache is that the basic method couldn’t be more simple and that the tradition has a very, very long history behind it. By “simple” I mean that it is simple in theory. To be an excellent practitioner of the method is something that few attain.
Gouache is, essentially, crushed natural pigments combined with a little white lead and then mixed with water. The addition of white lead is the reason that the paint is opaque. Remove the white lead and you have normal, transparent watercolors. A gouache painter can achieve quite remarkable subtleties of color; the cheeks in the above painting are evidence of that. Charles