Blue can be many things. An adjective for a colour - He saw the blue car An adjective for an emotion - He went off in a blue funk (here a blue funk means that the person is very angry) A noun -- They had a blue (here blue is slang for argument or fight) A blue can also be a name for a red haired person. As in "Hey, blue" Some of the Australian slang terms are not often encountered and you might be thought odd if you were to use them.

A "blue" can be a fight or argument. It can also be a nickname for a person with red hair (although this is a fairly old usage). Then there's our lovely expression, "true blue". :) Grab a hanky and Bundy for this: https://www.youtube.com/watch?v=ceWKrsJX9N4