Definition of true blues:
(adj) :
Steadfastly faithful or loyal; unwavering in loyalty; staunch, true.
(adj) :
Representing the true essence of something; authentic, genuine, honest.
(adj) :
Patriotic.
(n) :
(countable) A faithful partisan or supporter of a cause, person, political party, etc.
(adj) :
(specifically, Australia, informal) Representing authentic Australian culture, values, etc.
(adj) :
(UK) Of or pertaining to the (historical) Tory, and now the Conservative, political party; hence, steadfastly conservative.