The The Microtivity Site LEDs that I use are NOT diffused so while looking at the ping pong ball at about eye-level, the colors which are a mix of Red/Green/Blue are blended well. However, when looking at the ping pong ball closely or at below eye-level (i.e.: like passing under it going through the door), there are obvious "rings" of colors which appear at 3 distinct spots on the bottom of the surface of the ping pong ball.
In an attempt to make this more diffused, I put a bit of baking soda into the ball, and re-inserted the LED.
Unfortunately, it was obvious that there was a powder at the bottom of the ball once it had been hanging for a bit and the "dust had settled."
My next attempt (I'm an 'electrical' guy, not too 'mechanical') was to spray a coating of white Papilio Window Masking-Spray on the LED.