Im having a problem with animation QTs in fcp6. the alpha comes through alright and i have the alpha set to white. unrendered it looks fine. when rendered though the edges of the animation graphic go grey / white. The edges of the black animation are feathered and soft as its an animation of a creature.
Render alpha as straight for pristine results. Especially if you have feathered edges. It premiltiplies the edges with the actual color of the edges so you don't get any halo effect. What app did you use to create a premiltiplied with white alpha?