I've never used sandpaper, that would freak me out...hahaha

I use non staining colors if I want the white of the paper to show through after I rub off some of the color. Or I use a staining color for the base and rub of the additional layers...

I'm afraid sandpapering the paper would change the spread of the paint and it's color...I've never done this technique...

I will try it on a separate piece of paper to see how it works...lol