meiroo2 I understand your situation, but I don't think we know if it is necessary to separate all of the slots. I cannot say for sure since I don't know the whole image of your skeleton, but I think you can successfully change the color as they are without separating all of the slots, except for images that need to leave a pure white area in one part of the image, such as the eye. If you try it and something doesn't work, please ask us again.
