Seen amongst the cirrus ove Chichester today; the colurs haven't been captured on film as well as I'd like, but a broad section across the centre was quite strongly coloured.

See http://www.atoptics.co.uk/halo/cha2.htm.

Interesting points: it's seen directly below the sun which must be 58+deg above the horizon (Sorry, Edinburgh, you'll never see it - it's only possible for 100 hours a year even in London), formed by aligned flat hexagonal platesof ice crystals, rays of sun in at one side and refracted out through the base (diagram on website above)