colors imported step file, how to change

I imported a STEP file into Rhino. It was a block, but I exploded everything, so now all parts are separate surfaces. I want to change the color of the yellow part and make everything red. Additionally, I want to make one separate surface blue. So far, I've only managed to change the color of the edges, while the surface itself remains the same color. Does anyone know how to change the colors of surfaces without having to redraw everything?