WPF DatePicker textbox white border not editable

I am editing the control template for the DatePicker but there is an issue with the TextBox style. There is a white border around the text which IS NOT the actual TextBox border. With my current style, I have the TextBox inside a Border with the TextBox Background set to transparent and the BorderThickness set to 0.

<Border Grid.Column="0" 
        Height="25"
        Background="DarkKhaki"
        CornerRadius="5"
        Grid.ColumnSpan="1">

<DatePickerTextBox x:Name="PART_TextBox" 
                   Background="Transparent"
                   Grid.Column="0" 
                   BorderThickness="0"
                   Focusable="{TemplateBinding Focusable}" 
                   HorizontalContentAlignment="Stretch" 
                   Grid.Row="0" 
                   Grid.ColumnSpan="1" 
                   Margin="1.143,0,1.056,0"/>
                            </Border>

This is what the DatePicker looks like with this Style:

If I add a Border to the TextBox, it appears around the white Border:

If anyone has any idea on how to remove this extra Border it would be much appreciated!