Strange rainbow

Last weekend I was on Arran with some friends; we had an excellent time camping in Glen Rosa, despite the attentions of the midges on Sunday night. Something odd, though: when we arrived at Brodick on Friday it was dry but the mainland was getting rain. Nothing unusual about that, but what was striking (and something I have never seen before) was the wedge of rainbow colours between the clouds and the horizon. I took this photograph, which does not adequately capture, even with some enhancement, the vivid colours we saw but gives some idea what it was like: