Cook Islands pearls mirror the rainbow-like spectrum of colours found inside the mother-of-pearl shell. They are named black pearls for the shades of black on the outer shell and lip of the oyster. In the pearls the darker hues of black, blue, green and brown are prominent, while lighter colours such as white, silver, grey and gold are also evident.

Translucent, overlaying shades of aubergine, peacock green or lighter pastels are also found in higher quality pearls, giving them added depth and glow. Colour , like shape, is a matter of personal choice and taste. Colour does not influence the grading of an individual pearl but certain hues do attract higher prices.