The options -darkBackTextureFile and -liteBackTextureFile now also work in XBoard, similar to the way they do in WinBoard. Except that it accepts pixmap (.xpm) files, rather than Windows bitmaps (.bmp). I have also activated the -overrideLineGap option (although tuning the width of the grid lines has always been possible in XBoard as part of the -size option).
An example with marble texture and the built-in pieces:
