Calendar colours changing themselves
I've been using iCal on Macbook Air syncing the Calendar over iCloud to both iPad2 and iPhone5 for about a month.
I have two calendars - one was in Green and the other Orange (these were the default colours from when the devices were first used and I was happy with them so left the colours alone).
Two days ago the Green calendar started changing itself to Blue and the Orange one started changing itself to Purple. If I change the colours back to my desired Green and Orange (and I've tried doing it on all three devices) then they just keep changing themselves (on all three devices) to the undesired Blue and Purple.
Both the MBA and iPhone5 are one month old, and software is up to date on all three.
I'm aware of another (old) thread concerning colours and subscribed calendars, but these are not subscribed calendars.
MacBook Air (13-inch Mid 2013), OS X Mountain Lion (10.8.4)