The phrase "black zipper" refers to a fastening device made of two strips of cloth or metal with interlocking teeth, typically used on clothing or bags, that is colored black. Full definition
fitted mini skirt length with black zipper closure. (beaconscloset.com)
You can't really tell, but this one from Banana Republic has black zipper detailing on the sides, and allows for some versatility depending upon the weather. (oliverstwistblog.com)
I'm wearing Notion 1.3 brown teddy coat (old) / Thrifted mom jeans / Maruti black pony - hair ankle boots / Nelly black zipper bag / Unknown black sunglasses (old) / Asos polo - neck top (justlikesushi.com)