Definify.com
Webster 1913 Edition
True-blue
True′-blueˊ
,Adj.
 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
. True′-blueˊ
,Noun.
 A person of inflexible integrity or fidelity.