I already answered to this question in your support thread but I will copy my answer here so that it will be helpful to others from the community.
Regarding your first question - yes. You can bind the color of the RadTileViewItem header. Actually the header is represented by separate control and you can use a custom style targeting its background. You can find ready to run demo demonstrating this approach in our XAML SDK.
Regarding your second question - yes. You can control the size of the maximized RadTileViewItem indirectly. When you know that the maximized item takes all the available space for the RadTileView control you can change the size of the minimized items and the RadTileView itself to change the size of the maximized item. You can try using the following properties:
Please give this approach a try and let us know if you need any further assistance.
Pavel R. Pavlov
Check out Telerik Analytics, the service which allows developers to discover app usage patterns, analyze user data, log exceptions, solve problems and profile application performance at run time. Watch the videos
and start improving your app based on facts, not hunches.