Transparency of text boxes

Hi

Currently I use TextBoxes as a child to a StackPanel for displaying info in the chart window. I can't seem to be able to use transparency with it though. The new-ish indicator info at the top right does have this transparency though. What technique should I use to be able to have my text look like the indicator info text?

This is how I currently do it:

private TextBlock[] profitTextBlock = new TextBlock[4];
        private StackPanel profitPanel;


        Profits currentOpenProfits;
        Profits dailyProfits;

        protected override void Initialize()
        {

            currentOpenProfits = UpdateOpenPositionProfits();

            // Create StackPanel to contain the TextBlocks displaying the output
            profitPanel = new StackPanel
            {
                HorizontalAlignment = HorizontalAlignment.Left,
                VerticalAlignment = VerticalAlignment.Bottom,
                BackgroundColor = Color.Black,
                Margin = 5
            };

            for (int i = 0; i < profitTextBlock.Count(); i++)
            {
                // Configure each of the TextBlocks
                profitTextBlock[i] = new TextBlock
                {
                    Text = "",
                    ForegroundColor = Color.White
                };
                profitPanel.AddChild(profitTextBlock[i]);
            }
            Chart.AddControl(profitPanel);
        }

Which results in this:

Ideally, it would have an opacity or alpha setting so I can adjust the level of transparency.