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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)?

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    $\begingroup$ Afaik what's black is the coating on the aluminium, that helps the teflon stick to it. You know, teflon is very bad at sticking, so it needs a lot of help. ;-) $\endgroup$ – Karl Jul 25 '17 at 19:50
  • $\begingroup$ I agree with Karl. To get Teflon to stick to an aluminum surface, there are a few different techniques including sand-blasting the aluminum, applying resins to the aluminum surface, chemically modifying one side of the Teflon to make it more adherent, and combinations of these. Unfortunately I can't find any info on the specific appearance or color change from these process so can't fully answer the question. But given the changes made to the 2 materials (the Teflon and the aluminum) there is no reason to expect the appearance of the final product to resemble that of either unmodified product. $\endgroup$ – airhuff Jul 25 '17 at 22:08
  • $\begingroup$ As @Karl states, treatment of the Al-PTFE interface with reducing agent such as Na dissolved in NH3 to promote adhesion likely leaves some carbon particles. See books.google.com/… $\endgroup$ – DrMoishe Pippik Jul 27 '17 at 21:16
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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.

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