I don't believe normal VS does that sort of text highlighting for certain items. You must have some add-on in VS that adds it.
Anyhow this is probably what you need in your app's Resources to modify the item template:
<Style TargetType="editors:IntelliPromptCompletionList">
<Setter Property="ItemListItemTemplate">
<Setter.Value>
<DataTemplate DataType="editorIntelliPrompt:ICompletionItem">
<DataTemplate.Resources>
<editorIntelliPrompt:ImageSourceProviderConverter x:Key="ImageSourceProviderConverter" />
</DataTemplate.Resources>
<DockPanel>
<Image DockPanel.Dock="Left" Width="16" Height="16" VerticalAlignment="Center"
Source="{Binding Path=ImageSourceProvider, Converter={StaticResource ImageSourceProviderConverter}}" />
<shared:PixelSnapper Margin="5,0,5,0" VerticalRoundMode="CeilingToEven" VerticalAlignment="Center">
<editorPrimitives:IntelliPromptCompletionItemText Item="{Binding}" VerticalAlignment="Center" />
</shared:PixelSnapper>
</DockPanel>
</DataTemplate>
</Setter.Value>
</Setter>
</Style>
You'd probably have to replace our IntelliPromptCompletionItemText control with some control of your own that would switch foregrounds based on the bound ICompletionItem.