Design question - how do I get a gradient-like layer on a lightbox?

I'm trying to design a lightbox. I have a Snapmaker so multi color isn't a problem - I'm wondering if maybe I can just do some kind of dithering in both horizontal and vertical axes to accomplish a gradient like effect for a lightbox? I had considered using a gradient roll but that would only work in one axis... maybe put a very high TD white down as layer 1, then do the dithering behind that to hide some of the transitions. Anyone have experience with this?