Rare Colors (7.28)
Diamonds do occur in every color of the spectrum but some are extremely rare including Intense green, red and blue for example are for the wealthy buyers and collectors. The saturation, tone, clarity and cut specifications of the rare colors will have a dramatic affect on the value. Any valuable fancy color diamond should always be purchased from a knowledgeable, reliable source or with the presence of a GIA Origin of Color Report (or other reputable lab document) for the purpose of authentication. Otherwise assume the stone to have been artificially treated, which brings its value down dramatically. 
The above pics are courtesy of: https://www.leibish.com/
Of course we didn't touch on the combinations of colors which would include a primary color and a modifying color such as brownish-orange where the primary color would be orange and the modifying color would be brown which would have a negative impact on the final value. Sometime the colors might be evenly split and would be expressed as for example a green-blue instead of a greenish-blue or a bluish-green.