Is there any basis in canon for Fëanor and his followers wearing red? I know he and his sons have "tall helms with plumes of red", but that's the only mention of the colour in any sort of symbolic connection to them that I can think of.
Fëanorian Red
Jumping the Inbox queue for you because this is a fairly easy one to answer.*
You're right! The idea of Fëanor and his followers wearing red is fanon. I would speculate it comes from two sources:
1. The passage you identified
And Fëanor made a secret forge, of which not even Melkor was aware; and there he tempered fell swords for himself and for his sons, and made tall helms with plumes of red. The Silmarillion, "Of the Silmarils and the Unrest of the Noldor"
2. The fact that we do know Fingolfin's colours were blue and silver
But as the host of Fingolfin marched into Mithrim the Sun rose flaming in the West; and Fingolfin unfurled his blue and silver banners... The Silmarillion, "Of the Return of the Noldor"
The "blue and silver" banners are again referred to when Fingon is killed in the Nirnaeth, and in Fingolfin's duel with Morgoth his shield is described as blue.
















