What is a common characteristic of pearls cultivated in tropical waters?

The characteristic of greater variety of colors in pearls cultivated in tropical waters is indeed correct. Tropical waters, particularly those around the islands of the South Sea and Tahiti, host specific species of oysters that are capable of producing pearls in a wide range of hues, including not only white but also shades of gold, pink, and black. This diversity in coloration arises from the unique conditions of the marine environment, including the specific kinds of mollusks involved and the influence of iridescence, which can cause variations in how light interacts with the layers of nacre formed during the pearl's development.

In contrast, pearls produced in temperate waters typically exhibit a more limited palette, primarily in white or cream, due to the specific species of oysters available in those regions. Other options, such as consistent round shape or lower quality nacre, do not accurately represent characteristics associated with tropical pearls, as these pearls can often be found in various shapes and can possess high-quality nacre, depending on the cultivation techniques used.