To change the colors of the pie slices, you should use TKChartDelegate's chart:paletteItemForSeries:atIndex: method to return a palette item that suits your needs. The following code snippet will change the color of the slice at index 3 to yellow:
More info about custom drawing in TKChart you can find in out documentation.
I hope this helps. I will be glad to assist you if you need any help.
Regards,
Adrian
Telerik
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