Define patterns for the pie slices. PATTERN statements define a different solid color for each midpoint value. 
pattern1 color=black;       /* biofuels     */
pattern2 color=blue;        /* coal         */
pattern3 color=green;       /* gas          */
pattern4 color=gray;        /* geothermal   */
pattern5 color=lipk;        /* hydroelectric */
pattern6 color=lime;        /* nuclear      */
pattern7 color=cyan;        /* petro        */
pattern8 color=red;         /* other        */