Hey all try this out cause this is what worked out for me
I have been having my "work" ical switch back and forth between green and purple and it was annoying so here is what I did.
I turned off my icloud from my iphone, "deleting" everything in my ical on my phone. THIS IS A CRUCIAL STEP. It will prevent your phone or pad from constantly updating and making sure your faulty calendar is still available.
Next I went to my ical on my laptop and EXPORT my "Work" ical to my desktop. I created a "New Calendar" titled "Work1" and then IMPORTED my "Work" ical into "Work1." I now have BOTH "Work" and "Work1" on my ical loading up to icloud AFTER you REFRESH by right clicking on your calendars and selecting REFRESH. Next you need to go tohttps://www.icloud.com/#calendar and LOGIN. You will now have acess to your icloud and fiddle around with it. BOTH "Work" and "Work1" should be present now. Now in the bottom left it says EDIT. Click and then DELETE your "Work" ical. You can then EDIT the name of "Work1" to be "Work." IT should now be updated and your faulty "Work" or whatever is now removed.
LASTLY, go back to your iPhone or iPad and TURN ON your iCloud. Your iCal will restore and no more faulty changing colors. Best of luck!
Here is something a bit more simple than the above.
I just had the same problem. I went to the iCloud to change the colors back, but they would automatically change back.
Here's what I did:
1. Take your calendars offline in iCal
2. Export the calendars that change color to the desktop
3. Delete the calendars from both the iCloud and iCal
4. Create new calenders in iCal making them the color you want
5. Import the calendars from the desktop int your new calenders
6. Put your Calendars back online to sync with iCloud
See my post at https://discussions.apple.com/thread/5441510.
This problem appears to be due to iCloud servers and not individual devices. I was able to work around the problem without actually deleting ALL the calendars as some of the above suggestions might imply. Importing the calendars from the desktop as suggested by aguest is something I did not try, however. Might try that if my suggestions do not work. See post above.
This helped me out to get my Calendar back to blue!
I was a bit wary to do it since we use this agenda for our business appointments and i was afraid i might lose them all but it all turned out fine!
I think your post will help a lot of people untill apple fixes this bug.