Board Thread:Speculation House/@comment-3115535-20151022150055/@comment-26397825-20151027015832

Rubies are red, which is Ruby's main colour scheme. And in certain lights, a natural ruby can appear to be black - another part of Ruby's colour scheme.

Pyrrha is red haired because her name means 'falme-haired'.

Blake, who is based on Beauty and the Beast which has nothing to do with the colour black, has the colours black and purple because her last name is Belladonna, which gets purple flowers and black berries.

Mercury (the metal) is silvery in colour, which is why Mercury (the character) has grey hair and wears grey.

Everyone has multiple allusions, and quite often their names do tie into their colour schemes.