There are many ways to take it and there are of course many ways Dark Horse can appear and reappear in a dream but these are the two most common. A dream of a dark horse may seem frightening of course but there is a meaning behind it that goes deeper than what is on the surface.
Dreaming of a dark horse just means that you are thinking about majesty and general prettiness. Black beauty is the name of the horse you are thinking of probably. Horses are known for being quite majestic and very beautiful. If you have a dream in which you see a dark horse then it is probably because you have seen something very beautiful recently and this is why you are dreaming of this.
The mustang is usually seen as a wild animal too that despite how crazy and buck wild it is, also has a sense of beauty about it. These are not the kinds of animals that are shot or put down because of how wild they are. These are the kinds of animals that we admire for being able to be so free. Therefore to have a dream of a dark horse this means that the person dreaming feels so strongly about their sense of freedom hat it is all they can think about.