I'm not sure if this is because of the fact that these
are the only textures that are still in the .wal format
or if it's because they're solid color, but some times
lights, black walls, or other things that use the solid
texture color will be replaced with some completely
random texture, like a crate. I haven't seen this
happen with any other textures besides the solid white/
black/grey textures. A vid_restart usually fixes this.