Fill Background of a Control with Gradient

        /// <summary>
        /// Paints a gradient to the Control's background
        /// </summary>
        /// <param name="ctrl">Control that needs the brush up</param>
        /// <param name="color1">e.g. Color.FromArgb(120, 180, 255), or Color.Yellow</param>
        /// <param name="color2"></param>
        /// <param name="angle">0: horizontal, 45: top-left to bottom-right, etc.</param>
        private void PaintGradientBackground(Control ctrl, Color color1, Color color2, float angle)
        {
            Rectangle rect = new Rectangle(ctrl.Location, ctrl.Size);
 
            System.Drawing.Drawing2D.LinearGradientBrush gradBrush =
                new System.Drawing.Drawing2D.LinearGradientBrush(rect, color1, color2, angle);
 
            Bitmap bmp = new Bitmap(rect.Width, rect.Height);
 
            Graphics g = Graphics.FromImage(bmp);
            g.FillRectangle(gradBrush, rect);
 
            ctrl.BackgroundImage = bmp;
            ctrl.BackgroundImageLayout = ImageLayout.Stretch;
        }

Adding Text with different color styles in RichTextBox

        
        /// <summary>
        /// Writing to a RichTextBox in different colors should be easy enough. The intiuitional way would be:
        /// richTextBox1.Text += someText;
        /// richTextBox1.Select(richTextBox1.Find(someText), someText.Length);
        /// richTextBox1.SelectionColor = Color.Blue;
        /// Which works but gets messed up when other text is added to the RichTextBox.
        /// Adding SelectedText instead of just Text does the trick:
        /// </summary>
        foreach (string ws in WorksheetsRequired)
        {
            if (this.Worksheets.ContainsKey(ws))
            {
                string ok = "Worksheet " + ws + " found." + Environment.NewLine;
                output.SelectionColor = Color.Green;
                output.SelectedText += ok;
            }
 
            else
            {
                string error = "Worksheet " + ws + " could not be found." + Environment.NewLine;
                output.SelectionColor = Color.Red;
                output.SelectedText += error;
            }

            // scroll to bottom of rtb
            output.SelectionStart = this.richTextBox1.Text.Length;
            output.ScrollToCaret();
        }