Наконец я нашел исправление.Переопределил шаблон по умолчанию для элемента меню и добавил триггер, который, когда элемент меню отключен, меняет цвет текста жеста ввода на отключенный.я имею в виду изменение цвета ..
<ControlTemplate x:Key="{x:Static MenuItem.SubmenuItemTemplateKey}"
TargetType="{x:Type MenuItem}">
<Border x:Name="Border"
TextElement.Foreground="{DynamicResource SubMenuItemTextForegroundColor}"
Background="{DynamicResource FileMenuBackgroundBrush}">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto"
SharedSizeGroup="Icon" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto"
SharedSizeGroup="Shortcut" />
<ColumnDefinition Width="13" />
</Grid.ColumnDefinitions>
<ContentPresenter x:Name="Icon"
Margin="6,0,6,0"
VerticalAlignment="Center"
ContentSource="Icon" />
<Border x:Name="Check"
Width="13"
Height="13"
Visibility="Collapsed"
Margin="6,0,6,0"
Background="#C0C0C0"
BorderThickness="1"
BorderBrush="#404040">
<Path x:Name="CheckMark"
Width="7"
Height="7"
Visibility="Hidden"
SnapsToDevicePixels="False"
Stroke="#404040"
StrokeThickness="2"
Data="M 0 0 L 7 7 M 0 7 L 7 0" />
</Border>
<ContentPresenter x:Name="HeaderHost"
Grid.Column="1"
ContentSource="Header"
RecognizesAccessKey="{TemplateBinding Tag,
Converter={StaticResource TagToRecognizesAccessKeyConverter}
}"
VerticalAlignment="Center" />
<TextBlock x:Name="InputGestureText"
Grid.Column="2"
Text="{TemplateBinding InputGestureText}"
Margin="5,2,0,2"
DockPanel.Dock="Right" />
</Grid>
</Border>
<ControlTemplate.Triggers>
<Trigger Property="Icon"
Value="{x:Null}">
<Setter TargetName="Icon"
Property="Visibility"
Value="Hidden" />
</Trigger>
<Trigger Property="IsChecked"
Value="true">
<Setter TargetName="CheckMark"
Property="Visibility"
Value="Visible" />
</Trigger>
<Trigger Property="IsCheckable"
Value="true">
<Setter TargetName="Check"
Property="Visibility"
Value="Visible" />
<Setter TargetName="Icon"
Property="Visibility"
Value="Hidden" />
</Trigger>
<Trigger Property="IsHighlighted"
Value="true">
<Setter Property="Background"
TargetName="Border"
Value="{DynamicResource SubMenuItemMouseOverBackgroundBrush}" />
<Setter Property="TextElement.Foreground"
TargetName="Border"
Value="{DynamicResource FileMenuBackgroundBrush}" />
</Trigger>
<Trigger Property="IsEnabled"
Value="false">
<Setter TargetName="HeaderHost"
Property="TextElement.Foreground"
Value="#DDDDDD" />
<Setter TargetName="InputGestureText"
Property="TextElement.Foreground"
Value="#DDDDDD" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>