Issues with iCal

Hey everybody.

For a about a week now I have some issues with my iCal. Since I have plenty of meetings with different people, I decided to give every Calender a unique color. But now, iCal changed the colors all by itsself to default purple. I wanted to change the color via my iPhone, but it always changed back to purple by itsself. Then, I did it via icloud.com, and it happened again; as soon as I click on another color for a calender here, it changes back to purple. What could be the reason for that? Am I doing something wrong here?
Please help me out here, because always likes iCal for its colors.
Greetings