if you split the face with split lines, youcan apply different apperances to each face. though if someone looked close enough they could see the "inside" of your sticker.
alternately, you could make it a multibody part and apply different material or apperances to each body.
Did you try a "mask" type of operation wen applying the decal?
Thank you guys. I take there is a way then. Now I will take your guys' info and give it a whirl.