Update ColorPicker.xaml

src/WPFDevelopers.Shared/Themes/ColorPicker.xaml

@@ -150,7 +150,7 @@
                                                     <GeometryDrawing.Brush>
                                                         <LinearGradientBrush EndPoint="0,1">
                                                             <GradientStop Offset="0" Color="#00000000" />
-                                                            <GradientStop Offset="1" Color="Black" />
+                                                            <GradientStop Offset="1" Color="{StaticResource WD.BlackColor}" />
                                                         </LinearGradientBrush>
                                                     </GeometryDrawing.Brush>
                                                     <GeometryDrawing.Geometry>