No reason to yell, I was under the impression that the dialog for screen
resolution would allow you to change color depth as well.

I always just change my xorg.conf file to use the correct color depth.

I know it is in the UI somewhere, but I use Windows for my client on my laptop
and Ubuntu is my server, thus I never really see the interface anymore.

http://www.ubuntux.org/reset-xwindows-color-depth

That shows how to change the depth using the xorg.conf method.

I think, if I recall, you can find the option under the Administrator menu for
settings. It should be like "Displays" or "Configure Displays".

If you have an nVidia graphics card, you can also find settings using their own
configuration tool.

By the way, a simple Google search on "change color depth Ubuntu hardy" produces
several good web pages, trying more than your first page listing would have
taken you to the 5th entry which is the URL I have posted. Google is a
wonderful tool and if the first option doesn't work, perhaps try the 2nd, 3rd,
etc... Unless totally useless options are around I usually try at least the
first page of results and skim each one for keys to actually doing what I want
done.

You should try it, very handy.