Change SelectItem background color

 <Window.Resources>
        <SolidColorBrush x:Key="{x:Static SystemColors.HighlightBrushKey}" Color="Turquoise"></SolidColorBrush>
    </Window.Resources>

 /// <summary>
    /// Gets the <see cref="T:System.Windows.ResourceKey"/> for the <see cref="T:System.Windows.Media.SolidColorBrush"/> that paints the background of selected items.
    /// </summary>
    /// 
    /// <returns>
    /// The resource key for the <see cref="T:System.Windows.Media.SolidColorBrush"/> that paints the background of selected items. This brush's <see cref="P:System.Windows.Freezable.IsFrozen"/> property is true, so it cannot be modified.
    /// </returns>
    public static ResourceKey HighlightBrushKey
    {
      get
      {
        if (SystemColors._cacheHighlightBrush == null)
          SystemColors._cacheHighlightBrush = SystemColors.CreateInstance(SystemResourceKeyID.HighlightBrush);
        return (ResourceKey) SystemColors._cacheHighlightBrush;
      }
    }

 /// <summary>
    /// Gets the <see cref="T:System.Windows.ResourceKey"/> for the <see cref="T:System.Windows.Media.SolidColorBrush"/> that paints the text of selected items.
    /// </summary>
    /// 
    /// <returns>
    /// The resource key for the <see cref="T:System.Windows.Media.SolidColorBrush"/> that paints the text of selected items. This brush's <see cref="P:System.Windows.Freezable.IsFrozen"/> property is true, so it cannot be modified.
    /// </returns>
    public static ResourceKey HighlightTextBrushKey
    {
      get
      {
        if (SystemColors._cacheHighlightTextBrush == null)
          SystemColors._cacheHighlightTextBrush = SystemColors.CreateInstance(SystemResourceKeyID.HighlightTextBrush);
        return (ResourceKey) SystemColors._cacheHighlightTextBrush;
      }
    }