I've never had that issue before. The only issue I've run into is getting a shiny spot on them from where they've sat on the tinfoil when baking. An easy way to deal with that is to bake them on a paper plate.
The only thing the aluminum foil will do is make a shiny spot wherever the clay has sat on it.
Remember that different brands of translucent polymer clay will each look different. I've found that the Fimo brand of translucent works best for fruits.