Thank you) It' s very important for me!=)

As I know it means it happened suddenly I mean without any plan, or without you expecting it! I saw that they say " I saw my friend in the street out of blue" it means "i saw him without expecting to see him,otherwise he appeared in front of your eyes suddenly" or they also say " I don't like to go to the party out of blue" it means I don't like to go there without any invitation"! hope my words were clear and help a bit!