Pre-release snapshots of GNU Backgammon are periodically made available for FTP at ftp://alpha.gnu.org/gnu/gnubg/.
If you want to experiment with the very latest code, the development sources are kept in a CVS repository at http://subversions.gnu.org/cgi-bin/cvsweb/gnubg/; see the @gnubg{} web page at http://www.gnu.org/software/gnubg/gnubg.html for instructions on checking out sources from the repository.
Once you are running @gnubg{}, enter new game at the `(gnubg)' prompt to start a game against the computer opponent. You should now see a board (if an X display is available, @gnubg{} will use a graphical board window; otherwise, it will display an ASCII board on your terminal). If @gnubg{} won the opening roll, it will have moved; you can now type roll (or click on the dice below the board if you are using X) to roll the dice yourself. In either case, it will now be your move; you should enter the moves for each chequer as pairs of numbers. For instance, if you have rolled 3 and 1, you could type 8 5 6 5 to move one chequer from the 8 point to the 5 point and another from the 6 point to the 5 point. Use bar to move from the bar, and off to bear off. If you are using the X board window, you can also drag chequers around the board with mouse button 1. Click on the dice when you have finished.
The file `gnubg.bd' is the bearoff database that @gnubg{} uses to evaluate endgame positions. @gnubg{} will look for it first in the current directory and then in the installed directory (`/usr/local/share/gnubg/' by default).
The @gnubg{} distribution is set up to create `gnubg.bd' by itself during compilation, but it can be a slow process (taking half an hour or more, depending on the speed of your computer). If you would rather not wait to generate the database yourself, you can obtain a copy via FTP from ftp://alpha.gnu.org/gnu/gnubg/gnubg.bd.gz.
The file `gnubg.weights' contains the trained neural net weights for most of @gnubg{}'s position evaluators. Like `gnubg.bd', it should be kept in either the current directory or the installed directory.
You should be able to obtain a copy from wherever you found the @gnubg{} distribution. Future releases of @gnubg{} will allow you to start without any existing weights at all, if you want to train your own.
If you see this problem, your X server is probably using a PseudoColor visual, and is dynamically allocating colours to clients from a limited colourmap. On these types of displays, @gnubg{} tries to be a well-behaved client by using colours from the default standard colourmap. This will allow it to share colours with other clients that use the same scheme, which will help them all to use as many colours as possible without exhausting the colourmap.
Unfortunately, not all X clients use standard colourmaps. If other clients have been run before @gnubg{} and allocated most of the colours, then there may not be enough left for @gnubg{} to allocate a standard colourmap. If this happens, it will just take what it can get (which in the worst case might be black and white only). You can try to avoid this problem by running @gnubg{} before other colour-hungry clients, or by using the `xstdcmap' utility to install the default standard colourmap early in your session while colours are still available. Depending on your hardware, you may be able to configure your display to allow more colours, or use a DirectColor or TrueColor visual which should resolve the problem.
Of course, if your X server can only display black and white (not even shades of grey), then there's not much you can do!