If no
      background color is specified, then white is assumed. Note 4 Background color is the specified color of content over which the text is to be rendered
      in normal usage. It is a failure if no background color is specified when the text
      color is specified, because the user's default background color is unknown and cannot
      be evaluated for sufficient contrast. For the same reason, it is a failure if no text
      color is specified when a background color is specified. Note 5 When there is a border around the letter, the border can add contrast and would be
      used in calculating the contrast between the letter and its background.