Colour has repeatedly served as a fast, visible way to signal allegiance — in military uniforms historically, in the flags and rosettes of political movements, and in protest clothing chosen deliberately for visibility and solidarity.
Red has been used historically as a military uniform colour by various armies, including British 'redcoats', valued in part for visibility and the ability to distinguish friend from foe at a distance in the era before modern camouflage doctrine.
Notable use · Britain and other historical military powers · before modern camouflage doctrine
Political movements have long used specific colours as identifying symbols — red for various socialist and labour movements historically, for example — a practice that continues in modern political branding.
Notable use · global · 19th century onward
High-visibility colour choices in modern protest movements (such as specific coloured clothing or symbols adopted for a demonstration) serve a similar function to historical uniform colour: fast visual identification of a group at a distance.
Modern use
Historical claims above are scoped to a specific period, region or culture where relevant — none are presented as a single universal fact. See methodology.