How to change background color of Windows Phone Listpicker in FullScreen Mode
<Style TargetType="toolkit:ListPicker" x:Key="ListPickerStyle1">
        <!--<Setter Property="Background" Value="{StaticResource PhoneTextBoxBrush}"/>-->
        <!--<Setter Property="Background" Value="YellowGreen"/>-->
        <Setter Property="Foreground" Value="{StaticResource PhoneTextBoxForegroundBrush}"/>
        <Setter Property="FontSize" Value="{StaticResource PhoneFontSizeMediumLarge}"/>
        <Setter Property="HorizontalContentAlignment" Value="Left"/>
        <Setter Property="Margin" Value="{StaticResource PhoneTouchTargetOverhang}"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="toolkit:ListPicker">
                    <StackPanel>
                        <VisualStateManager.VisualStateGroups>
                            <VisualStateGroup x:Name="PickerStates">
                                <VisualState x:Name="Normal"/>
                                <VisualState x:Name="Expanded">
                                    <Storyboard>
                                        <!--<ObjectAnimationUsingKeyFrames  Storyboard.TargetName="Border" Storyboard.TargetProperty="Background"                                         Duration="0">                                             <DiscreteObjectKeyFrame                                             Value="{StaticResource PhoneTextBoxEditBackgroundColor}"                                             KeyTime="0"/>                                         </ObjectAnimationUsingKeyFrames>-->
                                        <ObjectAnimationUsingKeyFrames   Storyboard.TargetName="Border" Storyboard.TargetProperty="BorderBrush"  Duration="0">
                                            <DiscreteObjectKeyFrame  Value="Yellow" KeyTime="0"/>
                                        </ObjectAnimationUsingKeyFrames>
                                        <ObjectAnimationUsingKeyFrames   Storyboard.TargetName="Border" Storyboard.TargetProperty="BorderThickness"  Duration="0">
                                            <DiscreteObjectKeyFrame  Value="200" KeyTime="0"/>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                            </VisualStateGroup>
                        </VisualStateManager.VisualStateGroups>
                        <ContentControl   Content="{TemplateBinding Header}"  ContentTemplate="{TemplateBinding HeaderTemplate}"  
                                          Foreground="{StaticResource PhoneSubtleBrush}" FontSize="{StaticResource PhoneFontSizeNormal}" 
                                          HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"  Margin="0 0 0 8"/>
                        <Grid>
                            <!--<Border   x:Name="Border"   Background="Yellow" BorderBrush="{TemplateBinding Background}"  BorderThickness="2">-->
                            <Border   x:Name="Border"   Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding Background}"  BorderThickness="2">
                                    <Canvas x:Name="ItemsPresenterHost" MinHeight="46">
                                    <ItemsPresenter x:Name="ItemsPresenter">
                                        <ItemsPresenter.RenderTransform>
                                            <TranslateTransform x:Name="ItemsPresenterTranslateTransform"/>
                                        </ItemsPresenter.RenderTransform>
                                    </ItemsPresenter>
                                </Canvas>
                            </Border>
                            <Popup x:Name="FullModePopup">
                                <!--<Border Background="{StaticResource PhoneChromeBrush}">-->
                                <Border Background="Yellow" BorderThickness="200">
                                    <!-- Popup.Child should always be a Border -->
                                    <Grid Background="Yellow">
                                        <Grid.RowDefinitions>
                                            <RowDefinition Height="Auto"/>
                                            <RowDefinition/>
                                        </Grid.RowDefinitions>
                                        <ContentControl   Grid.Row="0" Content="{TemplateBinding FullModeHeader}" Background="Yellow" 
                                                          Foreground="{StaticResource PhoneForegroundBrush}" 
                                                          FontFamily="{StaticResource PhoneFontFamilySemiBold}" FontSize="{StaticResource PhoneFontSizeMedium}"   
                                                          HorizontalAlignment="Left"  Margin="24 12 0 0"/>
                                        <ListBox  x:Name="FullModeSelector" Grid.Row="1"  ItemTemplate="{TemplateBinding ActualFullModeItemTemplate}" 
                                                  FontSize="{TemplateBinding FontSize}"  Margin="{StaticResource PhoneMargin}" Background="Yellow">
                                            <ListBox.ItemsPanel>
                                                <ItemsPanelTemplate>
                                                    <StackPanel Background="Yellow"/>
                                                    <!-- Ensures all containers will be available during the Loaded event -->
                                                </ItemsPanelTemplate>
                                            </ListBox.ItemsPanel>
                                        </ListBox>
                                    </Grid>
                                </Border>
                            </Popup>
                        </Grid>
                    </StackPanel>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
	
using System.Collections;
using System.Windows;
using System.Windows.Controls;

namespace Microsoft.Phone.Controls
{
    public interface IListPickerPage
    {
        string HeaderText { get; set; }
        IList Items { get; }
        SelectionMode SelectionMode { get; set; }
        object SelectedItem { get; set; }
        IList SelectedItems { get; }
        DataTemplate FullModeItemTemplate { get; set; }
        bool IsOpen { get; set; }
    }
}
	
<toolkit:ListPicker x:Name="lpStr"
                    Grid.RowSpan="2"
                                    Width="1"
                                    Height="1"
                                    CacheMode="BitmapCache"
                                    ExpansionMode="FullScreenOnly"
                                    Foreground="Black"
                                    FullModeItemTemplate="{StaticResource ListPickerStringLargeTemplate}"
                                    IsHitTestVisible="False"
                                    Opacity="0"
                                    PickerPageUri="/Views/Globals/ToolkitPages/MyListPickerPage.xaml" />
            </Grid>