Yes, you can just partially freeze between layers. But if you are using a thick smoothie type mixture, you can do it w/o freezing if you are careful pouring it into the molds. I would start off with a light colored layer (maybe banana and yogurt), add strawberries to the blender to make a pink layer, then add blueberries or spinach to what remained in the blender to make either a purple or a green layer. That was easier than blending up separate batches. If you use frozen berries, the mixture will be stiffer from the get go and speed up the freezing.