Why are teflon coated dishes black or dark grey in colour when teflon as such is white (and the underlying aluminum is not black either)?
Note: I was employed at DuPont in the 1990's, and my understanding of Teflon(R) cookware manufacturing is based on proximity to product research and development and not from hands-on experience with PTFE formulations.
Teflon(R) polytetrafluoroethene coated materials are manufactured in several steps. The PTFE coating is specially formulated as a waterborne dispersion containing surfactants and pigments.
Versions of Teflon(R) coatings sold in the early 1990's used a primer/topcoat system to improve adhesion of the polymer film to the substrate. These formulated coatings are applied to the cookware and the pan is fired at high temperatures to form the PTFE film. Coatings can be applied to both grit-blasted and smooth substrates.
The color(s) observed on PTFE coated cookware results from interactions of the pigments, polymers and surfactants during the high-temperature curing process.