This must be the explanation as it was near evening when the phenomenon occurred.
Rainbow Visibility
Refraction and reflection in a raindrop, producing a rainbow.
Source: english wikipedia, original upload 01. Jan 2003 by en:User:DrBob
http://en.wikipedia.org/wiki/Rainbow
http://en.wikipedia.org/wiki/File:Rainbow1.png
Religion and mythology
Picture: Noah's Thanks Offering (c.1803) by Joseph Anton Koch. Noah builds an altar to the Lord after being delivered from the Flood; God sends the rainbow as a sign of his covenant (Genesis 8-9).
http://en.wikipedia.org/wiki/Rainbow
http://upload.wikimedia.org/wikipedia/commons/f/f5/Joseph_Anton_Koch_006.jpg
Rainbow diagram showing the conventional arrangement of colours: Red Orange Yellow Green Blue and Violet. The colours shown do not necessarily correspond to actual wavelengths.
A vectorized version of Rainbow-diagram-ROYGBIV.PNG
Source: http://en.wikipedia.org/wiki/Rainbow
http://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Rainbow-diagram-ROYGBIV.svg/800px-Rainbow-diagram-ROYGBIV.svg.png
Reference