the palette stored inside of .vxl files are not 18bit, they are 24bit. I came to the conclusion after writing my own renderer for the files, and tried to 18 to 24 bit palette conversion in XCC after seeing a post saying the palettes are 18bit somewhere, the colors came out all wrong, when i didn't use the conversion, the colors were all correct.

i'm betting the 18bit is only for the pal files, which are not needed to display the voxels