How to add colors for Charts in Numbers v6
I just filled  2 columns and 12 lines in a spreadsheet. I then made a donut chart as shown in the image below.



The chart needed more than 6 colors so some colors were repeated. I clicked on the chart once to select it and then clicked again on a colored segment. See next image



You can see here that I have selected one of the colored segments and slightly separated it.  Now I go to the Style tab at the top right of the Numbers file. You can see here where you can change the color of the segment. I changed one instance of light blue to bright blue, one instance of green to a dull green, one instance of gold to yellow and finally one instance of red to fusia. This final plot is shown below.