It looks like the tcl/tk resources are being set to provide a black UI - possibly in .Xdefaults/.Xresources. I think the black looks quite cool (apart from not being able to read some text
)
You can change this by editing tcl/ac3d.tcl
add a line at the start like this:
tk_setPalette #eeeeee
(the eeeeee is an rgb col, so you could use ff00ff etc. You can also use words like 'grey', 'red' etc)
This should work on any platform of AC3D e.g. Window and Mac too.
Andy