How to color beam emitter with gradient

hello ppl,

I would like to color my whole scene with gradient, but except one object - the background. I use post process material with image to get gradient and i put it on my plane which is connected to camera and i get gradient only on my physical object. Here is an example (without the background)

Gradient looks fine on these dots, but beams are simply white. Why?
Plus, I would like to have 100% white material on my background. Is there any way to achieve this?

cheers!