>I can't figure out how to add color to the rectangle.

On the menu bar, click on Format and Background Color. This will fill the rectangle with the color you choose. You may also want to change the Foreground Color (the 'outline' or 'border') to white, or matching the background.

The choice of words in the menus is not very intuitive, especially when you are thinking along the lines of setting properties in the Form Designer.

HTH,