Set -highlightMoveWithArrow true in the xboard.conf file, and specify a
lineGap of 0 to make that efficient (and the wood theme even nicer).
-bitmapDirectory ""
-liteBackTextureFile "/usr/share/games/xboard/wood_l.xpm"
-darkBackTextureFile "/usr/share/games/xboard/wood_d.xpm"
-bitmapDirectory ""
-liteBackTextureFile "/usr/share/games/xboard/wood_l.xpm"
-darkBackTextureFile "/usr/share/games/xboard/wood_d.xpm"
+-overrideLineGap 0
+-highlightMoveWithArrow true