A black MINI UPPER 2K part can have some odd effects when applying decorations. Namely, corrupting the colors of the arms and hands, often times switching them around in a variety of ways. One combination of changes resulted in part of the minifig's left arm turning into a sort of reddish pink color, with the color being referred to only as "??Material4??", with the numerical value assigned to it being, unsurprisingly, 4. Here is a picture of the color applied to a haripiece (which can be selected via the color picker tool):
Another thing happens when the colors manage to corrupt themselves into not obeying the lighting. When this happens and you try to select a decoration for the torso, some error pictures show up, but the decorations work as intended.
What are your thoughts on this? Why does this occur? Can this be useful, like when trying to get "illegal" colors?