THANKYOU!  I have been banging my head on the wall for weeks trying to resolve this... you have solved both my issues nicely.

Extremely grateful!

Indeed... the XamNumericEditor below the CellValuePresenter has FG color ...white (well, it's light grey actually... but looks white ;-)... and this value is flagged as "Inherited in Snoop's Value Source.  Inherited from where?   The object (CVP) at higher level  sets it red...(BTW... I am not expert in this stuff, forgive me if say something dumb!).  If I track back up the visual tree, I eventually see DataRecordPresenter with Foreground FontControlBrush set to the white(grey) color... but that's as expected... and wanted.  I do want (most) of my grid foreground white...  but added  this code to achieve the red negatives on just two fields

			Style redForegroundStyle  = mainpage.Resources["CVP_RedField"]  as Style;
			Style blueForegroundStyle = mainpage.Resources["CVP_NormalField"] as Style;
			dg1.DefaultFieldLayout.Fields["Profit"].Settings.CellValuePresenterStyleSelector =
				new CVPStyleSelector_Field(redForegroundStyle, blueForegroundStyle);
			dg1.DefaultFieldLayout.Fields["CNP"].Settings.CellValuePresenterStyleSelector =
				new CVPStyleSelector_Field(redForegroundStyle, blueForegroundStyle);

Plus this code... taken pretty much straight out of the Help page on Conditional Formatting:

		internal class CVPStyleSelector_Field : StyleSelector
		{
			private Style _redStyle;
			private Style _normalstyle;

			internal CVPStyleSelector_Field(Style redStyle, Style normalstyle)
			{
				this._redStyle    = redStyle;
				this._normalstyle = normalstyle;
			}

			public override Style SelectStyle(object item, DependencyObject container)
			{
				bool isneg = (0 > decimal.Parse(item.ToString()));

				if (isneg)
				{
					return _redStyle;
				}
				else
				{
					return _normalstyle;
				}
			}
		}

Finally... here's my XAML code:

  <Grid x:Name="mainpage" Margin="0,10,0,00" Height="Auto" VerticalAlignment="Stretch">
      <Grid.Resources>

        <Style x:Key="CVP_RedField" TargetType="{x:Type dp:CellValuePresenter}">
          <Setter Property="Foreground" Value="Red" />
        </Style>
        <Style x:Key="CVP_NormalField" TargetType="{x:Type dp:CellValuePresenter}">
          <Setter Property="Foreground" Value="Blue" />
        </Style>

I kinda said already... I don't really even WANT XamNumericEditor at all... NO EDITS... I just want to display the value red if negative - period.  In fact, I really WANT to get rid of the NumericEditor control... it just messes up my display when you click on it (I don't need/want that).

The other frustration for me is this:  I used exactly the same code in a standalone WPF app I cut... and it works perfectly.   Only difference is my real "app" is an embedded add-on in my trading platform... rather than a standalone WPF app.  See next pic...

Thankyou for your help...