If it had dark to light spots in both types of colorant my next question is does it have deep ribs or small or thin wall flow areas across the parts if so shooting slower or raising mold (steel) temps up. I’ve seen colorant do this from how it flows across the steel with both pellets and liquid colorants both of witch were fixed with a different shot speed normally slower and a higher steel temp. I had almost an exact same issue with a pellet we tried at the screw to fix it going so high on back pressure (with slower speeds) and saw improvement but never fixed it for more than an hour(also we bridged the feed throat) I did a doe involving steel temps and found it wasn’t that it wasn’t mixing properly at the screw but as we shot it the flow across the face of the tool was more of the issue