I've had lots of trouble with palladium. I apply 2-3 coats and fire it to ^6 with a 15 minute hold. It's usually that nice silver but is occasionally that ugly black. I have also found that it looks especially silvery under a clear glaze.
I have had very bad luck with potter's choice glazes. I agree they all turn out really dark and muddy looking. The only one I ever use is Palladium which i've had a lot of trouble keeping from running.