Auto changes colours in iCal
I have an iPhone, iMac and MacBook Air, my iCal is synced through iCloud and I have never had any problems with it before. But in this last week, one of my calendars has been changing from one colour to another, green to purple in this case. I'll change it back to green and within a few minutes it will change to custom purple. I have edited it on my phone as well and it reverts to this custom purple on there too.
Wondering what I can do to fix it.
MacBook Air (11-inch Mid 2012), OS X Mountain Lion (10.8.5), iPhone 5 iOS 7 & iMac OSX10.8.5