Aside from orbs and the occasional cupboard banging, shadow people are a common sign of a possible haunting. Due to the association with the color black and it’s association with evil many believe them to only be the sign of an malignant or evil spirit. I personally do not believe this to be true. Being made up only of energy (possibly) I can only imagine how difficult it would be to try and create a manifestation of oneself and yet not accidentally blink themselves out of existence. So the only way to appear and not tax themselves is to appeal as a shadow of their former self, no pun intended.
Mind you not all shadow people look like shadows. A loose definition for them would be any haze like form in the vague shape of a humanoid figure. While the most common seen is dark in tone they can appear in different colors and/or glow in the case of some in lighter colors. Sometimes they appear on their own, sometimes they’re accompanied by other signs that one is not alone. Many are unsettled by them many for the fact that it’s an invasion much like if a burglar were to break into their homes. It’s some one that is unfamiliar and strange.
The only thing is that in several cases the spirit isn’t invading as much as we the living are. For many of them it’s still their home and they’re not happy about the new guests. This reminds me of a similar story if I may go off track a moment. The meat of it all surrounded the spirit of an old man trying to kick a young couple out of his home. However they retorted that while it had been his at one time they needed shelter but since he was dead no longer required it. This sort of startled the spirit since he wasn’t used to being challenged and after a silence the three came up with compromise. The deal was so long as they had a room set aside for him and left a fresh flower in his memory they could all coexist.
Back to the original topic is that unless otherwise founded, one shouldn’t fear shadow people. They’re not all evil, plotting to steal our spleens at night. They’re just a manifestation of people still hanging about after passing.
Disclaimer: I can’t speak for everyone in this since my only experience on this count was when I was young and one peeked into my room. At the time I only thought that someone had broke into the house.