Great questions. I don't know any 100% for sure facts but can share this: During our Croaker testing the white belly with dark (normally green) top made at least a 200 - 300% strike difference. With solid colors they would still come check them out (get within 1-3' of it), but often would turn and head back in the grass. Do I think it makes a difference, I absolutely do in open water (i.e. throw in the grass and retrieve back into open water or around trees). I don't think it matters in the grass because they are striking the motion, not the bait.
With that said, I think the optimal pour is to hand pour the bottom vs, inject it as a laminate. Why, as Ted pointed out, a laminate is only one color on the bottom. A hand pour shows both, not sure color matters as long as they are contrasting. I have great confidence in the white belly with dark green contrast, but I'm sure other colors would work equally well or better when other conditions are factored in.
What do I know 100% for sure, I love me some frog fishing!
Tight lines,
Jason