Image_Graph_Common | --Image_Graph_Line_Solid | --Image_Graph_Line_Formatted | --Image_Graph_Line_Dotted
This style displays as a short line with a shorter space afterwards, i.e 1px color1, 1px color2, 1px color1, etc.
Image_Graph_Line_Dotted Image_Graph_Line_Dotted( mixed $color1, mixed $color2)