I set up a Prismatic Wall and a non-protected creature passes through it, say from left to right. On page 269 of the 5e Player's Handbook, the Prismatic Wall spell reads:
When a creature attempts to reach into or pass through the wall, it does so one layer at a time through all the wall's layers. As it passes or reaches through each layer, the creature must make a Dexterity saving throw or be affected by that layer's properties as described below.
The layers are listed from Red to Violet, so the enemy passed through my wall in that order and made it through. They are now on the right side, and I have contrived a way to push them back through the wall to the left side. Do I reverse the order they encounter the layers and go Violet to Red, or do I always go Red to Violet whenever anything passes through the wall?
In other words, does a Prismatic Wall have a "sidedness" to it, and, if so, when is that sidedness established?