They're randomly generated
Reload the page and you'll get new random colours. :-)
No reason for it other than this being the quickest way to do it, and without different colours it would be much harder to see where each duchy begins and ends.
One thing you might want to change depending on how important you think characters not knowing the Zuma's borders are is it shows their duchies which shows their borders. Otherwise it looks great and may be able to help with roleplay too.
