Mother of Pearl or Nacre appears in a variety of colors from white to black and nearly every other color in between. It derives its color from three sources: genetic make-up, food and trace metals in the water and lastly to a lesser extent depth and salt content of the water.

• The mollusk's genes are in part responsible for the color of the Mother of Pearl. A rainbow-lipped, or black-lipped oyster instinctively creates darker colors, whereas a white-lipped oyster makes lighter colors.
  
  
• Mollusks are filter feeders, sucking water in with their valves, extracting minute food particles from the water then ejecting the water out. Their diet consists of 'Phytoplankton', microscopic algae, and these algae differ according to season. In the Gulf of California the blue-green algae called 'Cyanophites' are abundant in winter, but in summer a golden algae called 'Diatoms' are more common. These different 'Phytoplanktons' provide the mollusk with materials that change the color of their shell and nacre.
  
  
• Some trace elements are acquired from the water, such as metallic ions, that help the Mother of Pearl gain its unique coloration. Iron can give a pink color, copper a green to blue hue, magnesium a yellow coloration etc.
  

The term 'Iridescence' is often appropriated to Mother of Pearl as well as to opal. Iridescence is a general expression used when describing the presence of a rainbow effect across the surface; this is produced by the interference or diffraction of light through the gems crystal structure.