I install my own version of lyx rather than debian's version.  To get
it on my gnome-panel toolbar, I therefore have to create a custom
application launcher for it.  Rather than use one of the standard
icons presented by the launcher creation tool, I click "browse" and
then go to the directory in /usr/local/share/lyx/images where various
lyx icons are stored.  When I do this, all of the choices of icons in
the menu are "grayed out", and I cannot select any one of them.  In
this particular case the icons in question have .ppm and .xpm formats.

A workaround is to not use the file browser and just type in the path
to the icon in question.  This works fine.

The problem isn't isolated to lyx -- similar behavior occurs with a
non-debian version of open office.

This seems like a really old bug.  It doesn't happen for me
in Squeeze... I can select any .xpm or .ppm on the
filesystem for a custom launcher.

However, there is one weirdness about this bug report, that
the reporter says they are clicking "Browse...".  But that
button is for browsing for a specific command, not an icon.
Since graphics files are not executable, they would be
greyed out.  You have to click on the icon itself in
Launcher Properties to pick a new icon.

Mark