When I first got Lydia I immediately equipped her with the Axe of Whiterun. Since the axe is enchanted, when it glowed in her hand I thought nothing of it. I've recently given her an un-enchanted warhammer that out dps's the Axe of Whiterun. No biggy. Except the warhammer also glows in her hands. The glow is colored red, if that matters.
Lydia has no enchanted gear on her at all. Her weapon glows when she wields it. Why?