The Usual Existence is the name of the plane of vision we live in. While every existence is connecting in terms of physical changes, the Usual Existence is the version of reality humans can see.
Existence refers to what we can see and understand, as it will not be fully realized as reality unless you can witness and understand it.
Ethereal creatures remove the version of their bodies in the Usual Existence, making themselves invisible to most humans.
Glimpses create minute tears in the Usual Existence which are repaired near instantly. A first experience happens to you in every existence, while later ones only happen to the version of your body in this existence. Only the mental part travels through all existence at all times, otherwise your body would not move properly and would cause a de-sync.
If your body gets damaged in any existence, every body will be. Meaning a de-sync can easily, I must stress very easily, kill you. Your body could fall off a cliff in a different existence, and you would never know. You'll just suddenly feel light, maybe even be able to float, and then fall to the ground with the force of a speeding bullet. De-syncing is the true cause of spontaneous combustion, and other strange random death phenomenon.
ERIE allows you to see glimpses constantly, because tears are purely mental. Every time you FEEL as if you've experienced something for the first time, a tear is created for a split second.
There is only one other existence, as far as we know, and it is called the Unusual Existence.
Colors are reported to be inverted in the Unusual existence, by the more trained people with ERIE. If you understand it, you can master it. People with ERIE can master their eyes and allow their sight to shift between the Usual and Unusual Existences.
I've gotten a chance to speak with the woman who originally described the Unusual Existance as inverted in color.
According to her, it's not so much the colors that are inverted, as are the reflection and absorption of the color in that reality. For example, an apple in the Usual Existence appears red because it absorbs all colors except red, which it reflects. However, in the Unusual Existence, the apple would only absorb red and reflect every other color of light shining on it. This would give the apple a sort of blue-green appearance.