I don't see it doing any harm or good. Eyeshadows are mostly made up of talc, or clay, with an added binder and some pigment. I would think if it were safe to apply directly to the skin it would do little if any harm in compost. Even if there was something in it that was borderline harmful, the volume would be so little that it would be rendered harmless. Of course I'm not a scientist or doctor so I could be wrong, but I doubt it.
