In transparent objects such as diamond, orange colors result from selective absorption of light. What causes the color orange in diamonds remains a scientific mystery. Gem scientists used to believe the orange color was caused by nitrogen. Harry Winston's, the owner of the pumpkin diamond, believes the Pumpkin Diamond's color is caused by hydrogen. According to Jim Shigley of the GIA "The scientific reasons for color in color diamonds are not always known. The reason orange diamonds are orange is probably because of hydrogen or nitrogen."
Astute collectors understand that pure orange represents a nearly impossible standard for a natural colored diamond.
Orange more often appears with color modifiers, such as yellow and brown. The Adamas Collection has a very interesting selection of oranges, from an autumn orange and a flame orange to a pumpkin and deep orange, the range of richness and vibrancy of different shades of orange in the collection give an important understanding of the different how the color orange appears in nature.