in blue—
1. wearing blue clothes:
- Kim was chatting to a girl in blue as she laid crackling thorns on a fire.
2. executed or finished in various shades of blue color:
- Finished in blue, this item comes complete with a comfortable head cushion.
in the blue—(NZ sl.) said of a failure or of smth. going wrong:
- An attack that broke down would be said to be “in the blue.”
See also: out in the blue / out of the blue.