Hi Jarak,
Can you please elaborate a little. In general the pie chart automatically distributes the fillings from the current palette to the data points that need to be displayed as pies. This is not a random process. If the palette has three entries: red, green and blue, the first pie will be red, the second green, the third blue, the fourth will be red again an so on.
Do you want to fix a color for a specific group? For example if you are sure that your data set contains say three groups: US, Europe and Asia you could be using the new data point conditional formatting and fix the colors for each group if expression. However this feature is not available in the current version of the chart. The new release of the SSRS Vision is expected very soon, and we can give you a beta if you need to test its functionality.
Best Regards,
Nevron Support Team