"once in a blue moon" is it possible for the moon to actually be blue every once in a while?
A 2nd full moon in the same month is known as a "Blue Moon." I highly doubt the moon will ever be blue in colour.
Sadly no. it's just an expression
Blue moon is a term used for a second full moon in a month, not the color of the moon.
No the term comes from there being to full moons in one month which happens from time to time