The precision with which a diamond is the cut is the most critical factor in releasing its "fire" and "brilliance". Since it is the only factor that humans can control, it may be the most important of the 4C's.

Fancy colored diamonds cut to the most ideal and accurate proportions, it may achieve maximum brilliance. A good cut gives a fancy diamond its sparkle and helps to bring out the most intense color possible.

When cutting color diamonds, the cutter have to consider its inclusions, which may help enhancing the diamond's color. Facets and angles also give color to a diamond, so the cutter must think about what shape would bring out the stone's best color.

An "ideal cuts" for colorless diamonds may not indicate as ideal for a fancy color stone. Colorless diamonds often cut into round shape to achieve maximum brilliance, among fancy color diamonds square radiants and ovals are the most prevalent.