Bitonal images are images that consist only of a foreground color and a background color. You can change the foreground color and turn the transparency of the background color on and off.
Bitonal raster images are images consisting only of a foreground color and a background color. When you attach a bitonal image, the foreground pixels in the image inherit the current settings for color. In addition to the modifications you make to any attached image, you can modify bitonal images by changing the foreground color and by turning on and off the transparency of the background.
Bitonal images and their boundaries are always the same color.