Rayman uses particulary complex blending (3-stage), this was mostly worked on in 1.3, its even better now in 1.4 (tinted background)... take a look with the Reference Rasterizer Rice (RRR).
You have a TNT? I remember discussing this exact issue with Jabo, I don't think the TNT could do it, the GF can... try validate blending or an older plugin (the skys are broken in b2, ug).