What does it mean when your character glows purple in dragon age origins

Your character will glow when under the effect of a spell or sustained ability. Without more information, it's hard to say which exactly, but it sounds like one of Leliana's songs is active. Check the icons on your character sheet, if they're all bonuses, then there's nothing to be worried about. If the visual effect is annoying you, I think there are mods to remove the effect.