The Collaborative International Dictionary of English v.0.48:

True-blue \True"-blue`\, n.
   A person of inflexible integrity or fidelity.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

True-blue \True"-blue`\, a.
   Of inflexible honesty and fidelity; -- a term derived from
   the true, or Coventry, blue, formerly celebrated for its
   unchanging color. See True blue, under Blue.
   [1913 Webster]

WordNet (r) 3.0 (2006):

true-blue
    adj 1: marked by unswerving loyalty; "a true-blue American"; "a
           reliable true-blue country club conservative"