How to change color of gridline of dynamic table created in rich textbox in WPF application

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C#

WPF

I am creating wpf application where in Rich textbox user can paste tables,which background should be black by default and font and border of rows, Columns in white color.

What I have tried:

IEnumerable table1 = richTextBox1.Document.Blocks.OfType<Table>();

foreach (Table tb1 in table1)
{
    for (int i = 0; i < tb1.RowGroups[0].Rows.Count; ++i)
    {
        TableRow currentRow = tb1.RowGroups[0].Rows[i];
        var brushConverter = new BrushConverter();
        currentRow.Background = (Brush)brushConverter.ConvertFrom("#FFe2e2e2"); // grey background
        currentRow.Foreground = (Brush)brushConverter.ConvertFrom("#FF000000"); // black text                 
        // currentRow.FontWeight = FontWeights.UltraBold;
        currentRow.FontFamily = new FontFamily("Arial Black");
        currentRow.FontSize = 16.0;
        currentRow.FontStretch = FontStretches.UltraExpanded;
        currentRow.FontStyle = FontStyles.Italic;
        currentRow.FontWeight = FontWeights.UltraBold;
        //currentRow.FontWeight = FontWeights.Bold;
    }
}