Similar figures could be cut out of plywood, painted and glued to the wall. Furniture also is available in a rainbow range of colors. One dresser, available through nmchild , has drawers of different colors, each with unmatched hardware. If you're not brave enough to experiment with paint on walls, floors or furniture, changing drawer pulls is a simple way to go. They come in all sorts of colors and shapes, including animals, tools and baseballs.
Finials can be a fun option for introducing shape.
Pottery Barn Kids sells a four-poster bed with interchangeable finials, including stars and moons. Sets of finials also are sold separately. In a recent Saks Fifth Avenue Folio catalogue, a bedroom with a baseball motif featured a painted iron, steel and aluminum twin bed with real baseball finials. If the posts on your bed are broad enough, you could easily attach baseballs or other favorite objects. Shapely lamps add a little glow and a sculptural effect.