The X11 version of Zoom 1.1.0 has an issue that can cause it to appear black on black. Oops: this was caused by a new preference in the OS X version not having an equivalent in the X11 version.
I've made a patch for this problem, which you can download here.
(Updated 13/07/07 to fix a further issue which could result in some games now having psychedelic colours. Sigh.)