Image 1: Hair shafts can be heavily pigmented. Imagine if this was fragmented and driven into the dermis, you could mistaken it for soot.
A forensic pathologist often takes a section of the skin around a gunshot wound to demonstrate the presence of soot and unburned gunpowder particles.
Beware, however, not all darkly pigmented material seen within the epidermis or dermis is soot. You must consider clothing fibers (if shot through clothing), tattoo pigment (if shot through a tattoo), disrupted hair shafts, bullet wipe, and other bits of debris that penetrated the skin. The best way to learn is to take a section of all gunshot entrance wounds so you can train your eye.