Rune Bolt

You may have wondered where the phrase 'out of the blue' or 'a bolt from the blue' comes from. Its origins are actually from Misthalin, from the humans who made their way through the mountains to Isafdar. On arrival, they would be ambushed by roving elves, some of whom would fire rune arrows and bolts. Elves are a stealthy bunch, so the first thing a human soldier might know about the ambush would be an arc of blue (the 'blue' being the rune metal). The soldiers would worry about being shot by 'a bolt from the blue', which is where the saying originated.

Also see 'the thin blue line' and 'screaming blue murder'.