Unfortunately, you cannot use SystemColors.ControlTextBrushKeyit because it is applied when the item is not selected, or when it is selected but inactive (your question is read as if you are only interested in the last one). However, you can do this:
<ListBox ...>
<ListBox.Resources>
<SolidColorBrush x:Key="{x:Static SystemColors.ControlBrushKey}">Red</SolidColorBrush>
</ListBox.Resources>
<ListBox.ItemContainerStyle>
<Style>
<Style.Triggers>
<Trigger Property="Selector.IsSelected" Value="True">
<Setter Property="TextElement.Foreground" Value="Blue"/>
</Trigger>
</Style.Triggers>
</Style>
</ListBox.ItemContainerStyle>
</ListBox>
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