Im making rounded corner graphics to set into my table corners.

Im making them mainly in black corners and white corners...

When i export the black corners, I use a nice neutral color as my transparency index color and when i place it on the page it blends nicely and smoothly.
However...Any white rounded corners i try to make are turning out ridged and edgy no matter what index color i use...

The only way i have been able to make them look clean and smooth is by exporting the rounded corner with the assumed background color background.

This takes away from its reusability...can anyone tell me how i can get my white transparency to stick?