I put the case on a plastic bag, I didn't have newspaper around me. Then I started just splattering paint on the phone case, because honestly I was just trying to make a paint splattered phone case (which I had done before, but I used nail polish instead). When I didn't like how the colors were turning out, I just decided to take the case and flip it over so the paint was facing the plastic bag and I just applied pressure to it, so the colors would spread.
This can be messy, so I hope you don't mind getting paint all over your hands and under your fingernails. After I applied the pressure, I turned the case over and ta da! My solid coring phone case was now a piece of abstract art!