Blackbox checkmark in checked menu item
<p>I'm having a weird problem with <code>MenuItem</code> objects that have <code>IsCheckable=True</code> - a screenshot is worth a thousand words:</p>

<p><a href="https://i.stack.imgur.com/KII2z.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KII2z.png" alt="Blackbox checkmark in checked menu item"></a></p>

<p>This looks very much like <em><a href="https://stackoverflow.com/q/20643480/1188513">Check Mark Showing as a Black Box in Menu</a></em>, except the accepted answer there, unless I misread it badly, suggests to tweak <code>ToolBar.MenuStyleKey</code>, which doesn't seem to be tweaking the right thing at all:</p>

<pre><code>&lt;Style x:Key="{x:Static ToolBar.MenuStyleKey}" TargetType="Menu"&gt;
    &lt;Setter Property="Background" Value="Yellow" /&gt;
&lt;/Style&gt;
</code></pre>

<p><a href="https://i.stack.imgur.com/usTwE.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/usTwE.png" alt="Yay, a yellow menu... still blackbox checked menuitem"></a></p>

<p>So, how do I get to that black box, and make it, say, <code>GhostWhite</code>?</p>