Selected item loses style when focus moved out in WPF ListBox

The answer referenced will in some cases solve the problem, but is not ideal as it breaks when the control is disabled/readonly and it also overrides the color schemes, rather than taking advantage of them. My suggestion is to add the following in the ListBox tags:

<ListBox....>
    <ListBox.Resources>
            <Style TargetType="ListBoxItem">
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate TargetType="ListBoxItem">
                            <Border Name="Border" Padding="2" SnapsToDevicePixels="true">
                                <ContentPresenter />
                            </Border>
                            <ControlTemplate.Triggers>
                                <Trigger Property="IsSelected" Value="true">
                                    <Setter TargetName="Border" Property="Background"
                                            Value="{DynamicResource {x:Static SystemColors.HighlightBrushKey}}"/>
                                </Trigger>
                            </ControlTemplate.Triggers>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
        </Style>
    </ListBox.Resources>
</ListBox>

What this will do is set the Highlight background color on the list box item whenever it is selected (regardless of the control state).

My answer is based on help from the answers already given to these answers, along with the following blog: http://blogs.vbcity.com/xtab/archive/2009/06/29/9344.aspx

If you're only setting the background color, try replacing ControlBrush for the ListBox, as per this answer.