Cloudy iridescence

 

Thin clouds of ice crystals

Thin clouds with small and uniformly-shaped ice crystals passing close to the sun diffract the sunlight and produce iridescence.  

 

 

A train of clouds

The intensity of the irisation increases as the clouds get nearer to the sun.  The clouds on the left are about 10 degrees away from the sun.  As this formation moves to the left, the clouds on the right will soon get to show off their pastel colors.