image() z-values beyond zlim

Dear useRs,

When plotting with image(), I would like the z-values
that extend beyond the upper zlim to be indicated with
one colour, or preferably with som sort of hatching,
as I'm printing in black and white.  By default these
values just show up as blank areas in the image.  I've
tried all sorts of things, but nothing seems to work
for me.

Any solutions would be greatly appreciated.

cheers,
Mikkel