This picture shows contrast because it has light and dark colors. The backgrounds the darkest colors and the crayons are the lighter colors. You can focus more on the crayons because of the bright colors that they display.
15+ DIY display case, Glass Shelves & Locking Hinged Door
Family Fun has an fun idea for your snowman party -- Snowman chair covers. They have a tutorial with a little sewing involved, but I think it would be a little easier to use a white pillow case and then glue some felt pieces and buttons or pom poms on.