I happened upon some wonderful abstract Photoshop brushes created by forty-winks who has an amazing gallery on devientART.com. Below is the result of a couple of hours of play … it includes one background and three transparent effects.

This is the background …


… and these are the effects. They include the background which is transparent, a background at 75% transparency, and a background at 75% transparency with a texture overlay. Everything was done in Photoshop CS5.