Why are the pans mostly black?
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.