Diagonal linear gradient with 0.5 Offset for White

   
  

<Window x:Class="WpfApplication1.LinearGradientBrushExample"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="LinearGradientBrush" Height="375" Width="300">
    <StackPanel>
      <TextBlock Margin="5,10,5,0"
        Text="Diagonal linear gradient" />
      <TextBlock Margin="5,0,5,5"
        Text="- with 0.5 Offset for White" />
      <Rectangle Width="100" Height="75" Stroke="Blue">
        <Rectangle.Fill>
          <LinearGradientBrush StartPoint="0,0"
            EndPoint="1,1">
            <GradientStop Color="Green" Offset="0" />
            <GradientStop Color="White" Offset="0.5" />
          </LinearGradientBrush>
        </Rectangle.Fill>
      </Rectangle>
    </StackPanel>
</Window>