When i do a diagram and have multiple colors of wires I can only use dark colors.  Light colors such as white and yellow do not show well when printed. If the line could be dark and the fill be a light color it would work. You have Stroke Color Stroke Width Stroke Style Stroke type Fill Color Using fill color fills in a trapezoid if the line has angles. If a line could be drawn with a solid color center (fill) (white) and the outside stroke edges a solid color (black) then we can use any color for a wire. .