As you may have well noticed, genres can perfectly be treated the same way we treat the entire gamma of colors, and even 1000x more complex. What I mean with that is the fact that we, as humans, try our best to sort out the different resulting arrangements and driving forces into different genres, though everything can easily be subjective and mixed up with other ones, independent from their origins (which is another factor).
What I find the most interesting about genres in music, though, is that music is also a language. If we treat music as a language, then we can determine other aspects that things like "colors" don't necessarily have. Just like languages, it would be extremely difficult to simply create any music that wasn't following the basic constructing elements as the rest. For example, even if you wanted to start a new genre from scratch, would you start by using the 12-tone, equal temperament tuning system? Would you be using evenly spaced rhythmic pulse? Which meter? Which instruments? Which harmonic structure? All of those can be the "ink and letters on paper" that we "write" in western music genres. And once you start putting those "letters" together, will your words and sentences, semantically, make sense to our society? If you are going to say "sentences" and develop patterns that people would normally understand, which is the part that you would innovate with? What tone are you going to use to say whatever you want to say, and is it being used already? This is why there is no easy way to imagine these hypotheses.
However, the closest I've seen anyone inventing a brand new genre is the avant-garde composers. Why? Because they absolutely threw tonal music, tuning systems, traditional harmony, and a whole bunch of other stuff to the trash, started doing their own thing, and called it "music." It was SO new that a majority of people, even today, still feel awkward by listening to this "language that they cannot understand." Those new genres put to the test what is really music, or what is really a genre, or what is really innovative. On the surface, the avant-garde may seem an "extreme" example, but if you think about it and analyze it in every musical aspect, it really isn't.