The idiom "true blue" refers to someone who is supremely loyal, faithful, unwavering, and steadfast in their support, beliefs, or commitments. Etymologically, the phrase originates from textile dyeing traditions in medieval England, where Lincoln textiles dyed with blue wool were reputed never to fade or lose their color, symbolizing genuine quality and permanence. Over centuries, the expression transitioned from describing durable fabrics into a popular cultural metaphor characterizing dependable friends, loyal supporters, and individuals of uncompromised integrity.