Which of the following is NOT a feature of watermelon tourmaline?

Watermelon tourmaline is known for its distinctive appearance, which features a unique color zoning that resembles the colors of a watermelon. This includes a pink central zone that is surrounded by a green outer layer. The characteristic color zoning is an essential feature of watermelon tourmaline, often including varying shades and distinct transitions between colors.

The feature of having a single color throughout does not apply to watermelon tourmaline. Instead, this type of tourmaline is appreciated for its vibrant and contrasting color bands, which are a defining quality. The presence of the pink central zone and the green overgrowth, along with the distinct color zoning, are all hallmarks of this gemstone. Thus, the lack of a single color throughout correctly identifies an incorrect characterization of watermelon tourmaline.