Format datgrid texbox cell based on value in DataTable

 In my financial application I have a DataGrid with a DataTable as ItemSource. I'm using the DataTable because of the flexibility to view queries with different number of columns. So, the viewmodel creates the DataTable. The AutoGenerateColumns="True" to support the flexibility. I added some logic in the UI to highlight negative values. The XAML code:

It uses a ValueConverter to determine if the cell is not empty and to set the Background color based on the value.

public class ValueToColorConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if ((value.GetType() == typeof(string)))
        {
            if (decimal.TryParse((string)value, out decimal decimalValue))
            {
                if (decimalValue < 0)
                {
                    return Brushes.Orange as Brush;
                }
                else
                {
                    return Brushes.White as Brush;
                }
            }
            return Brushes.White as Brush;
        }
        throw new NotImplementedException($"No conversion from type {value.GetType()} to a Brush");
    }
}

As a first step works fine with the following result:

However I profer to have a more subtile formatting, by just coloring the Foreground color of the textbox and with right alignment:

I could not find a way to format the TextBox of the cell.

How can you achieve it, preferably in XAML