I wonder if there's effect plugin that will let you do this:
Fill a sprite with a layer of tiled background, while preserving the sprite's alpha?
Something like the official Set Color effect, that will let you fill the sprite with one color, preserving the alpha layer.
No masking because the object needs to be layered, moveable over background.
The idea is to make a doll dressing app, which is more flexible than offering the clothes pieces in fixed colors/patterns you have created on beforehand.
This might be in wrong form, sorry if it is so. :)