How to split out layers of a primitive from blender?

This is a sort of combo 3d/2d q but since its heavy on compositing someone might know here. i’m looking for an easy way to split up the faces of a primitive or scene etc from blender in AE so i have full control over it.

For example: imagine a cube and each face is a color and you key it out so you can use it as a mask.

So far Ive had the best results using normals and key light, the only problem is on something like a cube three of the sides will be black, which kinda ruins the effect.

Anyone have any good ideas to make this easy? Maybe key light isnt right?