Step 2. Apply the Radial Gradient. Go ahead and change the Fill from Solid to Radial Gradient.
Step 3. Edit the gradient. Next edit your Gradient by clicking on the Edit button to bring up the Edit options. Click the left color swatch and select White. For the Right Color Swatch, choose a color of your choice for the sphere.
Step 4. Modify the gradient's position. Return to your shape and click the Paint Bucket Tool to bring up the Gradient Modifying handles.
Step 5. Adjust the gradient. Grabbing both the Circle and Square handles, adjust them so they match the image below. This creates the effect that the light source is coming from the top left.
Step 6. Add a drop shadow. Create a Perspective Shadow effect to finish off your sphere and you're all set:-)