International firm Pastor Geneve delivers high-quality colored diamonds to collectors across the globe. In determining the value of these rare gems, experts with the firm emphasize color saturation, color composition, quality, type of cut and size. The rarest colored diamonds, bluish green and purplish red, represent one-of-a-kind items born of intense natural processes, and as such, their value is determined largely by the price the market is willing to bear at the time they are sold. For other small stones with colors like cognac, chocolate and yellow, supply and anticipated demand more or less determine prices. Advisors with Pastor Geneve can help clients negotiate the technical aspects of colored diamond grading.Many of Pastor Geneve's partners acquire colored diamonds for the aesthetic character of the stones and for a long-term investment. Owing to the rarity of the gems, the supply continually dwindles as demand steadily grows, driving up prices. Over the last four decades, fancy blue gems have appreciated roughly 100 percent every five years, with fancy pink and yellow gems appreciating at a slower but still impressive rate.