What do I add to acrilic paint when doing an abstract art depth?

Acrylic paints are most difficult because when you start mixing colors for shading and tone to add depth or brightness, they get "muddy!"

I know in oils, raw umber will change depth of colors.

You can experiment and paint something simple, then use a wash (a diluted) bit of raw umber or a coffee brown over the entire painting. it may give the same effect as wax gives over painted furniture.

You can layer the paint; add shredded paper, sand, plaster of Paris, or another granular substant to the pain; or you can apply string, wood chips, or plaster by gluing it to the canvas, then painting over it. ☺️