Fire, Elements The Hermetic Order of the Golden Dawn assigns red to Fire in its elemental colouring, used for the fire wand, the fire triangle and the invoking pentagram of fire. The attribution is a nineteenth century ritual convention of that order, not an inheritance from classical sources.
Source The Golden Dawn: The Original Account of the Teachings, Rites, and Ceremonies of the Hermetic Order of the Golden Dawn, 6th editionIsrael Regardie
Fire, Tattvas In the tattva symbols used for scrying in the Golden Dawn, Tejas, fire, is drawn as a red upward triangle. This coloured geometric set reached Western ritual practice through the Theosophical current of the late nineteenth century and is not the form the tattvas take in Indian philosophical texts.
Source The Golden Dawn: The Original Account of the Teachings, Rites, and Ceremonies of the Hermetic Order of the Golden Dawn, 6th editionIsrael Regardie
Red is the vestment colour of Good Friday in the Roman Rite, and of Palm Sunday, the two days of the Lord's Passion. Black was widely used for Good Friday before the reform of the missal and is still met with in older usage.
Source General Instruction of the Roman Missal, third typical editionCongregation for Divine Worshipthe holders' own account
Red is the vestment colour of Pentecost in the Roman Rite, where it reads as the fire of the Spirit. The same colour serves for martyrs, where it reads as blood: one colour carrying two distinct meanings inside one rite.
Source General Instruction of the Roman Missal, third typical editionCongregation for Divine Worshipthe holders' own account
Rubedo, the reddening, is the final colour change of the Great Work and the sign of the completed stone. Read as a chemical claim it describes a real observed change of colour, which is part of why the sequence survived so long as a technical vocabulary.
Source The Secrets of AlchemyLawrence M. Principe
In Chinese five-phase theory red is the colour of the Fire phase, and Fire governs the south, summer and the noon of the day. The scheme is correlative rather than decorative: colour, direction, season, organ and taste are read together, so red carries the south rather than merely sitting beside it.
Source Science and Civilisation in China, Volume 2: History of Scientific ThoughtJoseph Needham