What does mottling describe in the context of gemstones?

Mottling refers to the uneven distribution of color within a gemstone, where patches or spots of color vary against a contrasting background. This phenomenon can create a visually striking effect but may also indicate variations in the material's composition or how it was formed. Mottled stones often display a mix of colors that can enhance their overall appearance, set against a different hue that helps accentuate these variations.

The other options do not accurately reflect the definition of mottling. A uniform color spread would indicate a consistent color throughout the gemstone, which does not involve the contrasting qualities seen in mottling. The brightness of a gemstone's surface pertains to its luster and does not relate to color distribution. Lastly, a cutting technique aimed at enhancing color would focus on how the stone is shaped or faceted rather than the natural color patterns present within the material itself.