The difficulty is that the colors you need are buried deep within the Menu theme styles. These theme styles are some of the most complex among those shipped with WPF. They consist of 10-20 styles and templates.

In general I recommend creating styles similar to the one in itowlson s answer because it allows you to adapt gracefully to the current Windows theme, replacing just the properties and templates that you want different and leaving everything else the same.

In your case, overriding the theme styles piecemeal by adding indivdual tags is likely to be an exercise in futility. Fortunately you don t need to do so.

Clearly you are actually trying to create your own custom theme from a user experience point of view, so why not actually create your own theme in code? You can do this easily by copying the theme from Aero or Luna (as you prefer) and changing whatever you want to get exactly the look you want.

This is very simple to do with Expression Blend. Just:

1. Create an empty window and add a Menu to it.
2. Right-click the Menu, and select Edit Control Parts (Template) > Edit a Copy....
3. In the dialog box, select Apply to All and click New beside Resource dictionary
4. Enter the new ResourceDictionary file name, such as "MyMenuTheme.xaml"
5. In your App.xaml, use the MergedDictionaries to include MyMenuTheme.xaml into your application resources

Now you can make any changes you want to MyMenuTheme.xaml to affect the appearance of all menus in the application. This file will be several hundred lines long but it is generally easy to find the correct settings to change. In your case it would be the various defaults for Background settings.

Note that if you don t have Expression Blend, you can also get the theme styles to start with using reflector and BAMLViewer, but that is much more work since you have to manually select the styles and other resources you need.

To set the background on all MenuItem instances, define a style for MenuItem:

<Style x:Key="{x:Type MenuItem}">
  <Setter Property="Background" Value="#2E404B" />
</Style>

You should be able to do the same for the Separator class to polish off the remaining bits, though due to contrast issues you might want to style the entire Template rather than just the Background.

Alternatively, you might need/want to hijack MenuItem.SeparatorStyleKey, MenuItem.TopLevelItemTemplateKey, etc.

Go to the App.xaml or use Ctrl+F and look for this sucker

<SolidColorBrush x:Key="SubMenuBackgroundBrush" Color="#FF9B9B9B"/>