Iridescent Brick Wall

Most walls carry a fixed palette. This one picks up whatever color is falling on it, so a room lit with green torches goes green and the same room lit by a gem in the ceiling shifts with it. Builders use it as a canvas: one wall material, any mood, controlled entirely by which light sources you hang.

Some worlds tuck it into jungle shrines, so if yours has any you can strip them and have a usable stack long before Hardmode. Otherwise you craft it, which is the only reliable way to get enough to wall a room of real size.