Soldato
Although no longer considered canon - thanks Disney - KotOR explained the blade colours as follows:
Blue - Jedi Guardian, focuses on lightsaber combat
Green - Jedi Consular, focuses on force usage
Yellow - Jedi Sentinel, mixture of saber and force usage. Probably fair for Rey, but you could argue the same for Luke who made his own green saber.
Red - Sith
Mace Windu had a purple saber simply because Samuel L. Jackson wanted to visually distinguish his character.
Probably no longer relevant to RoS though....
Thats actually a good catch, id forgot about the different blades based on style of Jedi. Pretty sure though that Kennedy/Abrams had no clue of this and just gave Rey a golden saber to represent she's bloody perfect at everything.