LUA defaults the higher value to 255. changing the opacity to 255 has no visable effect.
it also seems that the closer the colour gets to black the less visable it becomes. its like black can never be drawn as there is no colour.
That would also mean that the format is not strictly RGBO.
changing the material to: MPDBasefp_BG.material = MakeMaterial("",{0,0,0,255}) makes is completly opaque again.