Hi Daniele,
Can you start a new project and get the example to work that was posted in the Silverlight thread? By the way, the poster to the workaround there was the actual developer of the WriteableBitmap method. Then you can modify it to fit your particular goal, and along the way, discover what may be going wrong. Finally, copy the solution into your real project.
Another way to go about this is to create a Grid and set its background to a color.
-Mark
Mark Chamberlain Sr. Escalation Engineer | Microsoft Developer Support | Windows Phone 7
