This (via BT new sweep) shows just how silly things get in the world of copyright and trademarking.  In short, Cadbury's objected to a small firm using purple choloclate wrappers for their advent chocolates, so the C of E has got a bit hoity toity about Cadbury's using ecclesiastical purple*.  Last time I looked the C of E didn't own purple either.

* I would have to say I have never seen the Cadbury shade of purple in any ecclesiasatical context.  Think I might look for a preaching outfit in that colour to offend Cadbury's and the C of E equally...