Silverlight toolkit comes with about a dozen themes that anyone can use to style there applications. In the example I am posting I use four of them, A theme file is essentially a XAML file that contains styles for all native Silverlight controls as well as all Toolkit controls. Implicit style manager allows developers to dynamically (or statically) load a theme and apply it to any FrameworkElement in the visual tree.
There are only a few steps you need to do to implement this type of styling.
1. Download and install Toolkit.
2. Create new Silverlight application.
3. Create new folder under applications (UserThemes in my example) and copy some or all themes from toolkit (C:Program FilesMicrosoft SDKsSilverlightv3.0ToolkitOct09Themes is the default folder) into that folder. Once you include all the themes into the project, set compile action to Content.
4. Now write a few lines of code in key places to apply a chosen theme. Here is what this code would look like:
private void ApplyeTheme(string themeName)
Uri uri = new Uri(string.Concat("UserThemes/", themeName, ".xaml"), UriKind.Relative);
5. You can even allow application user to select a theme by creating for example a combo box loaded with available themes.
Implicit style manager does carry some overhead with it. To minimize the overhead try to use apply mode of OneTime. Ap0ply mode of Auto will watch for LayoutUpdated event and restyle attached element. If you use this mode, you can apply this code to your shell (outer application frame), and any loaded control will be styled. It sounds easy, but it will slow down your application.
As you can see, you cheaply and easily implement dynamic styling using free! software from Silverlight Toolkit.
You can download full example here.