WPF DataGrid two lines with one color

Datagrid Row style

style

 <Style  TargetType="DataGridRow">
            <Style.Triggers>
                <!-- Change colors between lines -->

                <Trigger Property="AlternationIndex" Value="2" >
                    <Setter Property="Background" Value="#f4f9ff" />
                </Trigger>
                <Trigger Property="AlternationIndex" Value="3" >
                    <Setter Property="Background" Value="#f4f9ff" />
                </Trigger>
                <Trigger Property="IsSelected" Value="True">
                    <Setter Property="Background" Value="#ffeedb"/>
                </Trigger>


            </Style.Triggers>
        </Style>

Set up DataGrid attribute

AlternationCount="4"