Sets the color to use for drawing row and column dividers in the headings. Set this to the color number of the desired color. The color ignores the grid's foreground and background intensity — it is treated as the final color value. Accepted values range from 1 (black) to 16 (bright white). When this property is set to zero (the default), the dividers in the headings are drawn using the same color as the dividers in the rest of the grid.