In recent years, people have been using the name Blue Moon for the second of two full moons in a single calendar month. An older definition says a Blue Moon is the third of four full moons in a single season. Someday, you might see an actual blue-colored moon. The term once in a blue moon used to mean something rare. Now that the rules for naming Blue Moons include several different possibilities, Blue Moons are pretty common!
http://earthsky.org/space/when-is-the-next-blue-moon
The month of July 2004 has two full moons, which means one of them is a Blue Moon. But will it really be blue? Believe it or not, scientists say blue-colored moons are real.
http://science.nasa.gov/science-news/science-at-nasa/2004/07jul_bluemoon/
Nasa talked. In other words one of the your Gods!
Now all you shut up and count your salary !
Did you miss this part in what you linked:
"
One way to make a blue moon: use a blue filter. That's what Kostian Iftica did on July 2nd when he photographed this full moon rising over Brighton, Mass."
That is the description for this picture in the article:
"
But will it really be blue? Probably not. The date of a full moon, all by itself, doesn't affect the moon's color.
The moon on July 31st will be pearly-gray, as usual. Unless....
There was a time, not long ago, when people saw blue moons almost every night. Full moons, half moons, crescent moons--they were all blue, except some nights when they were green.
The time was 1883, the year an Indonesian volcano named Krakatoa exploded. ....Plumes of ash rose to the very top of Earth's atmosphere. And the moon turned blue."
"The
key to a blue moon is
having in the air lots of particles slightly wider than the wavelength of red light (0.7 micron)--and no other sizes present. This is rare, but volcanoes sometimes spit out such clouds, as do forest fires:"
Blue moon is an expression to express rarity of an event. It's orgins is somewhat questionable and used to mean something was absurd.
From what I can find for the phrases origin:
"The first known recorded use of a form of the phrase is in an anti-clerical pamphlet published in 1528 by William Roy and Jeremy Barlowe."
It was to express the absurdity of believing things that simple observations prove are false.
It finally became to mean something rarely happening since the moon can appear to be blue during very specific and rare circumstances that were recorded and documented later in history.
Seems when the moon appears to be blue it is for the same reason the sky appears to be blue.
I am thinking since English is not your native language somethings are being lost to you in translation.