Plastic Opacifier: recommended source?

I am searching for a good source of information for plastic opacifiers.

I am working on a product that will incorporate some LED backlite light pipes. The problem is that the light from the LED’s is bleeding through the polypropylene housing. Does anyone know if there is an additive for polypropylene that will make it more opaque or will I need to switch to an ABS for the housing material?

Any help with the subject would be greatly appreciated.

I’m not too sure of your exact application, but could you just paint the light pipes or coat them in shrink tubing?