Answer:
If one does not believe in the spirit world, then I suppose that it would seem to be science fiction, but for those who know of the spirit world, it is very real, with the physical world being outside what is considered "normal," as well as being a very boring place!
The current use of indigo is far from its original meaning, which was some with a deep connection to the spirit world. In its original meaning it had nothing to do with how anyone behaved, what size eyes they had, or any other behavioral or physical characteristics. It has to do with the ability to link with the spirit world. This, of course, is nothing new. There have been shamans, medicine people and seers since the beginning of time. What is new is that people who frame the world through the lens of western culture are now speaking of it with more acceptance.
If one believes that we each have a soul, then it is not a vast jump to believe that we can be in touch with our soul, an energetic part of us. Our souls are able to be connected with all things, thus making information available to us that the five senses cannot provide.
Sometimes people's intuitive abilities are out of control and they cannot tell the difference between what is from the physical world and what is from the spirit world. Sometimes empathic people absorb so much from others that they are unable to handle the energy and feelings. Some churches recognize that people can be possessed by other entities, although not like it is presented in Hollywood. These things can be handled by simple training and gaining an understanding of how to manage one's abilities.
Anyone who has ever gotten a "bad vibe" off a place or person is using their intuition. Anyone who gets a sense that something good or bad is going to happen if they go a certain place or associate with certain people they do not know well is getting information from the spirit world. Hollywood has done a lot to skew the perception of what linking with the spirit world is like, although the show Medium is pretty accurate.
There are many who claim to be intuitive, but are not. There are many who say the words that are related to knowing about the spirit world, but do not have an understanding of how it all works and thus do great harm to others. These people, naturally, cause doubt and suspicion about the whole matter.
In many native traditions, in regards to those who have abilities, they do not speak of what they can do. They do not call themselves shamans or medicine people. They live an humble and simple life and face trials just like everyone else. They certainly do not ask for hundreds or thousands of dollars to tell you your future or make things happen. There are many things that cannot be spoken of until someone has the training to handle the information and the information is seldom transmitted via words. It is important to work with someone who can keep you safe if you wish to understand your own ability to link with the spirit world.