TimePicker: Fix an issue with the Background property (patch #11288).

ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/DateTimePicker/Themes/Generic.xaml

@@ -111,7 +111,9 @@
                                 <Border BorderThickness="1" Background="{StaticResource PopupBackgroundBrush}" BorderBrush="{StaticResource PopupDarkBorderBrush}" Padding="3">
                                     <StackPanel>
                                         <Calendar x:Name="Part_Calendar" BorderThickness="0" />
-                                        <local:TimePicker x:Name="Part_TimeUpDown" 
+                                        <local:TimePicker x:Name="Part_TimeUpDown"
+                                                          Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"
+                                                          Foreground="{DynamicResource {x:Static SystemColors.WindowTextBrushKey}}" 
                                                           Format="{TemplateBinding TimeFormat}"
                                                           FormatString="{TemplateBinding TimeFormatString}"
                                                           Value="{Binding Value, RelativeSource={RelativeSource TemplatedParent}}"

ExtendedWPFToolkitSolution/Src/WPFToolkit.Extended/TimePicker/Themes/Generic.xaml

@@ -101,7 +101,10 @@
                                     <ColumnDefinition Width="*" />
                                     <ColumnDefinition Width="Auto" />
                                 </Grid.ColumnDefinitions>
-                                <local:DateTimeUpDown x:Name="PART_TimeUpDown" BorderThickness="1,1,0,1"  
+                                <local:DateTimeUpDown x:Name="PART_TimeUpDown" 
+                                                      BorderThickness="1,1,0,1"  
+                                                      Background="{TemplateBinding Background}"
+                                                      Foreground="{TemplateBinding Foreground}"
                                                       ContextMenu="{TemplateBinding ContextMenu}"
                                                       AllowSpin="{TemplateBinding AllowSpin}"
                                                       Format="{TemplateBinding Format, Converter={StaticResource TimeFormatToDateTimeFormatConverter}}"