A monochromatic color scheme really works well for an apple body shape. Wearing the same colors on the top and bottom creates a clean, straight line that lengthens and slims the overall silhouette of the body. The best way to be expressive with this look is to mix up the fabrics.
Try a combo of cotton and chiffon for a fun, light, flirty look. For a more serious look, try a sold-colored, tweed suit. On the other hand, you can try wearing two different variations on one color. For example, dark blue on bottom and a lighter blue on top still gives you the same straight line and let's you vary your style just a little.