I was struggling with this one for quite a long. You can't really have different color all together as per region. But you can surely have them shaded. What I mean by shading different is Dark Blue, Light Blue, more light blue and so on.. Trust me this look beautiful instead of having altogether different color. For me it looked something like this:
All you need is do is reduce the Opacity of color in Pie-chart Mark Type.
This would make the inner most circle darker and lighter shades towards the outer rings.
I couldn't open your workbook because it's made in a version later than what I have in my system, else could have attached the workbook with solution.
Let me know if this works.
Thank you so much for the help. Really appreciate it!
I am glad, I could help. If that solution worked for you, could you mark the answer as "Correct Answer". This would let others help in future.