Transparent Brushes
All elements in XAML including all brushes have an Opacity attribute that defines the transparency of an element. The value of Opacity is between 0 and 1. The value 0 means an element is fully-transparent and value 1 means an element is fully opaque. The default value of Opacity is 1.
The following code snippet creates a SolidColorBrush with 50% transparency. You can set the Opacity attribute of any brush using same code.
Figure 34. A rectangle with a transparent Visual brush in Tile mode
Transparent Controls