Although I am not sure what exactly you see as a tile, I believe that the issue might be coming from the format of the iconic tiles you use.
When you pass an iconic tile to Windows Phone, it converts all colored pixels to white pixels and then displays the converted tile. So if you have a square tile without transparent pixels, the result will be a white square. If this is what you're seeing, then what you need to do is to have a transparent background and color only these pixels that you want to be displayed from Windows Phone.
Please give this a try and let us know if it helps.
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