Why are the pans mostly black? Most pans are black (arbitrary example: https://www.hood.de/i/pfanne-20-cm-81718656.htm ). What advantage does a black pan have as opposed to other pans? Why are there fewer gray pans, aluminium pans or white pans? Why?
Teflon* is black therefore all Teflon pans are black. 

Other things are other colours, aluminium, copper, steel, so the outside may vary, but if it's Teflon-coated… it's gonna be black inside.

*Other non-stick coatings are available;)
Ceramic can be white, there's a stone/copper one which is brown/orange or grey speckled, anodised aluminium is dark grey.