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 layer settings for color. In addition to the modifications you can make to any attached image, you can modify bitonal images by changing the foreground color and by turning the transparency of the background on and off.
To change the foreground color of a bitonal image, use the Color property. To turn the transparency on and off, use the Transparency property.