That sounds like the same problem I am experiencing with 2-color GIFs
and Mosaic for X 2.1. They were fine in 2.0, but now they display as
blank on monochrome screens and sometimes blank/sometimes just faint grey
(depending on the image) on color screens. I'd bet this has something
to do with the GIF89 enhancement.
I notified NCSA (but I can imagine they are pretty busy right now) and
I have a test page setup on <http://www.ics.uci.edu/Test/> if anyone
wants to try their hand at debugging. Please let me know the results.
....Roy Fielding ICS Grad Student, University of California, Irvine USA
(fielding@ics.uci.edu)