I think with the recent updates Apple got rid of 8-bit color support. I too have Fallout 1 (Mac version) and it no longer works. For me I get the "Duck, and coverrr!" thing and the loading screen then it's all black but still with sound.
Only way to play Fallout 1 now is either to use Crossover/Parallels/VM/Boot Camp and run the Windows version... or hope Apple realizes it's still needed for some things.
Note: On Crossover, Fallout 1 for Windows works great but the cursor movement is slow as all hell.