I feel the dark symbolism has a lot to do with people reclaiming the title of witch. If you look at the way most people imagine what they believe the sterotypical image of a witch is, the modern day witch will happily embrace that and go with it. Given the rise of social media, there are many witches out there who play with the aesthetic.

The wearing of black clothing is because the colour black absorbs energy and light (it's also practical as it saves having to make complicated wardrobe choices ).
Horns are a symbol of deity, there are many pagan gods and goddesses who are horned, and skulls have many meanings in witchcraft, the deepest being a reminder that life is a temporary state.

None of it is dark symbolism, its actually very sacred to a lot of witches (although it could be misunderstood by those who don't fully understand the path and the history of witches and their craft).

To answer your main question I believe there is a difference, depending upon the practitioner (it can be a fine line) between black magick and magick that incorporates darkness, but wearing black clothing and horns or the use of skulls has no bearing on whether this type of magick is practiced.