I am not a Mac owner, but perhaps you try to run the game with the wrong screen resolution? (LCD screens are often less flexible w.r.t. resolution).
In openttd.cfg, there is an entry
(for playing at 640x480 obviously).
You may want to check/modify that setting.
Alternatively, you can remove openttd.cfg altogether (or rename to some other name), and see what happens.
Last but not least, it doesn't really look like an openttd problem, the game seems to run, except you cannot see anything. Maybe in a more Mac-oriented forum, they know what to do with blank screens?
Albert