Over time, paint oxidizes and becomes thin. The grey and green mold wash is the way to go but, To start off with the pink shouldn't be just painted solid two coats of pink. It should be watered down over a tan or light grey base and then sprayed with water (any household spray bottle) as it sets to bring out the base color here and there, thin over here and so on. Then go for the washes over that.
Other wise a solid pink will yeild a crappy brown grey with just a wash and become known as the pepto bismal room. Some washes may actually have a white tone depending on what kind of lights the scene will have. Really watered down like, spray with water then splatter or get some to run then more spray bottle action.
It is also possible to mechanically sand away the pink to show the base color. Most sand paper however leaves some of IT's undesireable color behind.
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