GradientStop.Color
expects a color, not a brush. Use PhoneChromeColor
and PhoneInverseBackgroundColor
instead:
<UserControl.Resources>
<Style x:Key="Divider" TargetType="Rectangle">
<Setter Property="Height" Value="2" />
<Setter Property="Fill">
<Setter.Value>
<LinearGradientBrush StartPoint="0,0" EndPoint="1,1">
<GradientStop Color="{StaticResource PhoneChromeColor}" Offset="0.0" />
<GradientStop Color="{StaticResource PhoneInverseBackgroundColor}" Offset="1.0" />
</LinearGradientBrush>
</Setter.Value>
</Setter>
</Style>
</UserControl.Resources>