Try it: Customize the Thumb element of a SimpleSlider
It is easy to customize the appearance of a Thumb control in Microsoft Expression Blend, by using the SimpleSlider control template.
Draw a SimpleSlider on the artboard in Expression Blend.
The simple style controls are available under Simple Styles in the Styles category of the Assets panel. After you select a simple style control from the list, you can draw it on the artboard.
Right-click the slider in the Objects and Timeline panel, point to Edit Template, and then click Edit Current. If you do not want to change the SimpleStyles.xaml resource dictionary, you can click Edit a Copy instead of Edit Current to create a new template and save it in the document. For more information about creating a copy, see Create a resource.
To exit the template-editing mode and return to the scope of your document: click Return scope to, which is above the element tree in the Objects and Timeline panel.
To return to template editing mode for an existing template: in the Objects and Timeline panel, right-click the element whose template you want to edit, point to Edit Template, and then click Edit Current.
Right-click the [Thumb] element in the Objects and Timeline panel, point to Edit Template, and then click Edit a Copy.
By default, the Thumb template contains a Grid that has an Ellipse. Delete the Ellipse element.
Double-click the Grid element in the Objects and Timeline panel so that you can add child elements to it.
Draw a path into the Grid element by using the Pen tool in the Tools panel. You can modify the path by using the Direct Selection tool to adjust points on the path.
To zoom in on the artboard, you can use the Zoom text box at the bottom of the artboard, or you can use the scroll button on your mouse while holding down the CTRL key.
As an alternative to drawing a path element by using the Pen tool, you can use an art resource that you import from Microsoft Expression Design, or an image file that you add to your project.
Test your application (F5) to see the effects.