The Rare Colors of Noctilucent Clouds

[Rick]

The electric blue color of Noctilucent clouds, or night shining clouds, are only visible in a deep twilight. From near the edge of space, the meteorological phenomenon shines when the Sun's rays hit them from below while the lower atmosphere is in darkness. They are the highest clouds in the Earth's atmosphere, located in the mesosphere at altitudes of around 75 to 85 kilometers (47 to 53 mi), and are not fully understood as meteorological phenomenon. Clouds generally are not able to reach such high altitudes with such thin air pressures.

More: http://www.colourlovers.com/blog/2008/09/27/the-rare-colors-of-noctilucent-clouds/

(This is an artists blog, and a bit script-crazy...)

[Rick]

In olden times, the spectre was considered to be of supernatural origin and fearfully ominous in nature.  Today, the phenomenon is known as a "Brocken Bow," named after a mountain in Germany.  Like a small, circular rainbow, a foggy Brocken Bow tends to last from several seconds to fifteen minutes.  Bands of color surround the gigantic shadow at a distance of several feet.  The outermost band is red, and the others follow the order of the typical rainbow.  In some cases, a Brocken Bow is surrounded by a second bow, whose color order is reversed.  A similar phenomenon, known as a Glory, is distinguished by the fact that the bands of color touch the head of the shadow.  Glories typically sport seven bands of color and can last for hours at a time.  Sometimes Glories are surrounded by glowing white fog bows.

More: http://www.colourlovers.com/blog/2008/08/07/spectral-colors-of-brocken-bows-and-glories/