Iv thought about this many times too, and i'm sure were not the only ones.
It would be great to see an actual Gold dye in game, Yellow on Paragon armour looks gold and shiny.. so why can't other classes have that colour?
/signed
Whether something looks gold (or silver) depends on the surface texture of the armor you're applying it to. If you put yellow on something metallic, it looks like gold... thus its easy to make gold armor for Paragons and Warriors. Similarly, silver only looks metallic on metallic armors as well. If you put silver on a cloth armor, it just looks like a light bluish-gray color. Anyway my point is dye cannot and (likely) won't be able to change the luster on a set of armor.
i personally hate gold. i put silver+brown on my paragon to achieve a more copper-looking tone because black is way overdone.
also, i don't see why gold would be rarer than black or white, because of the fact that it is literally impossible to create a universal black or white with other color combinations, while it is much easier to create a gold for almost anything.