At the wet-in-wet painting techniques we are using the drying time of paint to achieve a special effect.
Add the paint colors next on top of each other on the surface.
Go with a brush or cloth over the wet surface.
A handy option is to bring varnish during rubbing on the paint with each other , so that at te same time a protective layer added.
The longer rubbing the paint by each other, the more the colors mix with each other. So to find a medium fitted for your background.