People who consider themselves as part of the Goth scene usually prefer to wear black clothing and makeup. So, why do Goths wear black?

Black is a symbol of death, darkness, the mysteries of the universe. All of these things are themes of Goth music and art. Hence, the color just works for the theme of being Goth.
However, each Goth is their own person and they probably have different reasons for wearing black. It could be an expression of how they feel, they could be mourning, or they could just like black.
And, black isn’t the only color that Goths wear. There are a few different types of Gothic style and these incorporate colors like red, purple, pink, green, etc.

“Black was already the color that punks mainly wore. Goth developed from punk, in fact, if you look up the earlier goth outfits from the 80’s they’ll seem like punks but with more PVC and makeup. Apart from that, black is mostly associated with rebellion, melancholy, and, at least in Western countries, death, and funerals.” – Quora
Wearing black went on to become the easiest way to identify one as a member of the Goth subculture. If you want to dive into the world of Goth, A good place to start is The goth Bible: A Compendium for the Darkly Inclined.
Another way of thinking is that Goth is more defined by the way you think than by the way you dress There are Goths that dress in all white and you’d still recognize them as Goths without a doubt. The same is true for Goths that use neon colors.
So, you can put on a black t-shirt, black pants and a pair of boots and be Goth. However, you can also wear a Victorian corset with red lace and a red taffeta mini skirt with platform shoes and still be Goth. So, you don’t necessarily have to wear black.