_Trip_, did you notice a difference in the initial paste consistency between green skin and white core? I wonder if the core powder absorbs more water (since the plant stores water there), and the green skin paste comes out wetter if using the same cacti-powder:water ratio for both sections of the plant.

If so, when using whole plant, the diameter of the cactus would matter (powder from thicker cacti needing more water and vice versa). The outer skin only powder would be the lowest cacti-powder:water ratio, perhaps it needs to be less than 3 to avoid off colors (the green color is rinsed away easily, I'm referring to brown colors and even stickiness or goo in extreme cases).