'Run off into the Blue'

[davem]

into the blue
At a far distance; into the unknown: spontaneously take a trip into the blue.

out of the blue
1. From an unexpected or unforeseen source: criticism that came out of the blue.
2. At a completely unexpected time: a long-unseen friend who appeared out of the blue.

As has been stated, it means going into the unknown. But you have me intrigued. Why is the unknown 'Blue'? Blue is the colour of the sky, the sea & of the far distance (a blue haze on the horizon). Of course 'heaven' is blue & 'heaven' can refer to paradise, the sky or as a euphemism for the OtherWorld. Possibly in origin it referred to going into Faery/crossing into the otherworld?

Possibly not....

Cross-posted with Mith..