The compound "true-blue" originated in 17th-century Britain, directly referencing the unwavering colorfastness of a specific blue dye used by Scottish Presbyterians and later by the Tory political party. The term leverages the literal stability of the color "blue," which resisted fading, as a metaphor for the figurative quality of being "true" or steadfast. Thus, the logic progresses from a literal description of a reliable dye to an abstract characterization of absolute loyalty, whether to religious convictions, political ideologies, or personal allegiances.

Structure: true (genuine) + blue (color) true: From Old English trēowe, trīewe (faithful, trustworthy). Functional role: Adjective root conveying genuineness and fidelity. blue: From Old French bleu, of Germanic origin. Functional role: Noun/adjective root, here used symbolically to denote constancy and steadfastness.