PALVERS is a lump allowing to define texture replacement for paletted versions of truecolor graphics. This can be used if a truecolor texture does not convert well to the game palette with the built-in closest match method, so a replacement graphics can be provided. Sprites and HUD elements are not affected; only skies, flats and wall textures are substituted.
The syntax is extremely simple, merely a list of truecolor and paletted texture names, for example:
rgbtex1 paltex1 rgbtex2 paltex2
The vid_nopalsubstitutions console variable can be used to disable PALVERS-based substitution.