What does true-blue mean?

Answer 1

If you are speaking about people it is some one that is trustworthy, honest, genuine good person

the true color.

The term comes from the American Civil War. We sometimes refer to the Civil War as the "Battle of the Blue and the Gray", but initially at least, that wasn't always the case. The main military units in the war were regiments sent from the various states. Initially, each state outfitted their soldiers as they saw fit, which led to some unfortunate confusions. A few northern states sent units outfitted in gray, while a few southern states sent units dressed in blue. This caused several cases of "friendly fire" accidents on both sides, until both armies proscribed uniform rules. In the meantime though, the Union soldiers had begun to refer to those Union forces dressed in blue as "True Blue" to distinguish them from the southern soldiers dressed in blue. As a result "true blue" came to mean anyone who was through and through on your side.