Many have noticed and pondered the mystery of the 08 Castle sets: Why are some of the skelies black?
I haven't heard any real theories, but I did hear mention of possible racism (jokingly), which I'm sure is false. So, I've created my own "story-line" reason for the black skelies, and it's really pretty simple: They're charred! The "Evil Wizard's" lair seems to be in a volcanic environment (like most evil guys) and it seems likely that while this Necromancer was creating his skeletal horde some of the dopey bone-bags may have tripped, resulting in a fire/lava blackened soldier. After the first few fell in the Wizard probably would have realized the helpfulness of burnt skelies, being that fire hardened materials withstand more, and would have started "accidentally" giving his cohorts a magma-bath.
Anyway, that's my explanation for the skeletal mystery. Have a better idea? Post away!