A bastardization of two contradictory terms. True Blue is a dated naval/sailing term meaning honest and loyal to a unit or cause. Blue Falcon is used in the modern Army to designate a "Buddy F**ker", that is someone who is not a team player and displays no unit loyalty. Implies a more negative meaning when the terms are put together in this way: True(as in real,bigtime) Buddy F**ker.
Seaman Smith is True Blue. He took a cannonball to the testicles but still managed to crack a smile when the Queens knickers caught fire.
Private Tickle is a Blue Falcon. He ate a piece of pie at dinner chow and the drill seargent smoked the whole platoon.
Private Englund is a True Blue Falcon. She f**ked her country.
Two gay pining characters from some sort of media. The trope is generally associated with friends/enemies/lovers. Some examples include:
Keith and Lance (Voltron: Legendary Defender)
Adora and Catra (She-Ra and the Princesses of Power)
Asami and Korra (The Legend of Korra)
Ruby and Sapphire (Steven Universe)
Tony Stark and Steve Rogers (Marvel Cinematic Multiverse)
Ash and Gary (Pokemon)
Light and L (Death Note)