Sunburst graph - different shade between inner and outer circles

Hi 

I wonder whether I could adjust the different shades of colours between inner and outer circles. Currently, my graph looks like this. Both inner and outer circles are in the same shade. How can we differentiate between inner and outer circles?

I have found the sample work 

Whenever I select one colour for each category, the rest of items under this category will follow this colour. I have no idea of how to select different shades of colour for inner and outer circles.