SolidColorBrush described using 6-digit hexadecimal notation.

   
 

<!--The first pair of digits describes the amount of red in the color,
the next pair describes the amount of green,
and the final two digits describes the amount of blue.
-->
            
<Window x:Class="WpfApplication1.ShapesWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="ShapesWindow" Height="160" Width="400">
      <Window.Resources>
        <Style TargetType="{x:Type Rectangle}">
          
          <!-- Gives all the rectangles in this panel a white stroke. -->
          <Setter Property="Stroke" Value="White"/>
          <Setter Property="StrokeThickness" Value="1"/>
        </Style>
      </Window.Resources>
    <Canvas>
      <Rectangle Width="50" Height="50" Fill="#0000FF" />

    </Canvas>
</Window>