A colourful corona in front of the Sun is produced by the diffraction of light by small water droplets or ice crystals of the clouds. See the shadow of the plane's contrail and also a wasp under the Sun.

Canon EOS 550D, 23/10/2011 14:03, Shutter Speed 1/4000, Aperture Value 11.0, ISO Speed 100, Lens Canon EF28mm f/1.8 USM, Focal Length 28.0 mm