MultiValueConverter not working as expected

Question

I am trying to implement a "dirty flag" of sorts in my WPF Application, and I am running into some problems. I have a data grid, and one of the columns allows users to edit the Value property of an item of a custom Device class. In the future, the application will be linked to a database, so I want the user to be able to save changes to the database with a save button, which I have implemented. While the user has unsaved changes, I want the foreground of the value to be in red.

I tried solving this with a MultiValueConverter, as seen in this SO question, but it is not working as expected. Here is the class containing my converter:

public class MvcForeground : IMultiValueConverter
{
    public object Convert(object[] values, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        var changed = Brushes.Red;
        var unchanged = Brushes.Black;

        if (values.Count() == 2)
        {
            if (values[0].Equals(values[1]))
                return unchanged;
            else
                return changed;
        }
        else
            return unchanged;
    }

    public object[] ConvertBack(object value, System.Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

And here is the entire XAML for my DataGrid. I don't think all of it is relevant to this issue, but I don't know for sure, so better to include it:

<DataGrid Margin="20" AutoGenerateColumns="False" Name="MasterDataGrid" ScrollViewer.VerticalScrollBarVisibility="Visible" SelectionChanged="MasterDataGrid_SelectionChanged" AlternationCount="2" DockPanel.Dock="Top" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" >
        <DataGrid.Columns>

            <DataGridTextColumn IsReadOnly="True" Header="Name" Binding="{Binding Name}"/>


            <DataGridTemplateColumn Header="Value">
                <DataGridTemplateColumn.CellEditingTemplate>
                    <DataTemplate>
                        <Grid FocusManager.FocusedElement="{Binding ElementName=textBox1}">
                            <TextBox Name="textBox1"  GotFocus="TextBox_GotFocus"  Margin="0" Padding="-2" MaxHeight="29"  Text="{Binding Path=Value, Mode=TwoWay, UpdateSourceTrigger=Explicit}"/>
                        </Grid>
                    </DataTemplate>
                </DataGridTemplateColumn.CellEditingTemplate>

                <!-- This is probably the relevant bit -->

                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding Path=Value, Mode=TwoWay,UpdateSourceTrigger=Explicit}">
                            <TextBlock.Background>
                                <MultiBinding Converter="{StaticResource MvcForeground}">
                                    <Binding Path="Value"/>
                                    <Binding Path="Value" Mode="OneTime"/>
                                </MultiBinding>
                            </TextBlock.Background>
                        </TextBlock>
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>

            <!-- End Probably Relevant Bit -->

            <DataGridTextColumn IsReadOnly="True" Header="Default Value" Binding="{Binding DefaultValue}"/>
            <DataGridTextColumn IsReadOnly="True" Header="Minimum" Binding="{Binding Minimum}"/>
            <DataGridTextColumn IsReadOnly="True" Header="Maximum" Binding="{Binding Maximum}"/>


        </DataGrid.Columns>

        <DataGrid.GroupStyle>
            <GroupStyle ContainerStyle="{StaticResource GroupHeaderStyle}">
                <GroupStyle.Panel>
                    <ItemsPanelTemplate>
                        <DataGridRowsPresenter/>
                    </ItemsPanelTemplate>
                </GroupStyle.Panel>
            </GroupStyle>
        </DataGrid.GroupStyle>

</DataGrid>

According to the question I linked, that solution should work fine, but for some reason only the unchanged state ever registers(The foreground, and background when I experimented with that instead, is only black, never red).

Now, the answer I linked is almost 9 years old, and I expect much has changed in WPF and C# since then. I have no idea how these MultiValueConverters work, so My first instinct is to say that the problem lies in the values array passed into the Convert() method, as I have no idea where that is called.

That, however, is just a beginner's guess. Any help is greatly appreciated.

P.S. Yes, I do have the converter referenced in <Window.Resources>