According to naharisv.com, gold symbolizes love of spirit, the primordial yearning towards the essence. Meaning, purpose, awe and spiritual love are it? qualities. All quests of the heart are associated with the color gold. Wealth of spirit and civilization conjure gold.
Gold goes with everything and has an ancient connection to the hearts desire for power and spiritual mysteries. Gold conjures the beautiful sculptures of Egyptians, the Pre Columbian masks, the civilizations known for mystic powers, high mathematics and profound sciences. Gold is the color of attainment and profound concentration.
In Japanese Anime, Silver usually represents strong power. Sailormoon's image color is silver, and it is evident ( in the manga anyway ) that she has the potential to be more powerful than Galaxia. Silver to gold. Just like with the Silver Crystal, being more powerful than the golden crystal. The same can be said for Sailorcosmos - Silver ( soldier of the universe ) then Sailorgalaxia - Gold ( soldier of the galaxy ).