so I was thinking of a design in my head and wanted to know i anyone has ever tried it or if it even make sense....lol

I was thinking of covering the cake in 1 color of fondant then taking a different color of fondant and cuting out star or circle shapes and taking the piece of fondant with the shapes cut out of it and putting it over the 1st layer of fondant so you can see the 1st color of fondant showing through the 2nd layer.

or a 2nd way i was thinking of doing it was taking a sheet of fondant and cutting out the star and circle shapes and taking small pieces of fondant in different colors and roll them over the cut out holes so when you turn the fondant over you can see the different colors through the cut out spaces.

Has anyone ever tried this tecnique before??

I've seen this done on Ace of Cakes, when they do window on buildings. However, they cover the cake in black, then whatever color the outside of the building is, then cut out the holes in the top layer so the bottom layer shows through. I think if you try to cut out the shapes before you put it on the cake, they will distort as you are picking up the fondant and smoothing it over the cake.

yeah, you really would have to do 2 layers of fondant and cut the shapes from the outer layer after it is on the cake. Or, I have seen (if the BC underneath is crusted or cold as to not cause a problem) cutting the shape out of your single layer of fondant, then cutting the same shape from a 2nd color of fondant and inserting it in the hole.

I've seen it done with a polka dot design, but I can't remember where. I'll see if I can find it again.