Which of the following is a special pigment that contributes functional properties?

The special pigment that contributes functional properties is categorized as "functional." These pigments are designed not only to provide color but also to enhance specific characteristics or performance of the paint. For example, they can improve durability, corrosion resistance, opacity, or provide other beneficial properties such as UV protection or thermal insulation.

In contrast, the other types of pigments do not inherently contribute to the functional properties of the paint. Metallic pigments are primarily used for their aesthetic qualities, providing a shiny or reflective finish, while inert pigments generally serve to add bulk or opacity without affecting the properties of the paint. White pigments are primarily used to achieve brightness and opacity and thus do not have enhanced functional characteristics like the special pigments classified as functional.