Because the plastic is slippery and has certain properties a lot of inks will just sit on top and smear when they're touched. That's why it's important to use a permanent ink like Staz-On or a brand that dries quickly and doesn't smear. My Favorite Things has one that I like.
It's really easy and quite beautiful. Here's the finished card.
I put some foam tape around the scalloped frame with the colored acetate. It's slightly raised up from the card base. The flower almost looks like it's floating. A really neat effect.