Let’s take a minute to walk without using Express Design to create a logo for your Windows Phone application. Expression Design is included in the Expression Suite – it is NOT included with the free version of Expression Blend (which is included in the Windows Phone SDK).
When you submit your application to the marketplace, you will be prompted to provide a certain set of images. These are the required images at the time of submission.
This is displayed when your application is presented to the desktop Marketplace
This is displayed when your application is presented to the phone Marketplace
This is displayed when your application is within a list on the phone Marketplace
This is used as your application’s icon when it is Pinned to Start
This is used as your application’s icon when it is in the Program List
Choosing your Icon Design
In the images above, see how the color changes? This icon has a transparent background. When rendered, the accent color becomes the background. As a result, white a reliable primary color in your icon design. Full color icons make your application’s tile stand out. However, simple, white icons make your application look like a Windows Phone application. Choose your icon wisely.