What paths do these skins use? Usually it appears black in Magos if the model misses allocated skins and the correct textures path are not set accordingly.
Correct again, it appears as a green-violet checkered cube in editor and invisible in-game(most of the time) if that model has missing textures that either haven't been imported or the texture paths are set incorrectly.
Now, you can either check the paths for those textures using Magos's Texture Manager or this
program.