Get some fresh fixer on that immediately. If the frame edge is not
transparent, the film is under-fixed. Your fixer is probably exhausted.

I believe that 120 format Delta 3200 is on the same thick grey film
as the 35mm version. This can look pretty grey if you are used to
the clearer film base used on most other 120 format films. There
is probably some fog also because it is such a fast film, but I've
shot a few rolls of 120 format Delta 3200 and it always looks
pretty grey.

Try making some prints and see if you like the results.

If you are really worried, you might try clipping a small amount
off the end of the next film you develop, and fix the small clip
of film without development. This will show you how much of the
grey colour is in the film base. The film base is certainly greyer
than most other 120 films. (If you develop film with the bit of
tape still attached, you may find you already have a bit of film
underneath the tape which is pretty much unprocessed, and you
could peel off the tape and stick that piece in the fixer until it
clears.)

Peter.