Haven't used 400TX but I believe it's wholly antihalation
layer. In any case it's normal. Same thing with T-max
where presoaking has always yielded a dark purple color.

You may also notice a slight purple color after fixing.
I understand this is a sensitizing dye but should wash
out with adeqaute fixing and washing. If it doesn't you
should refix in fresh fixer.

Kodak changed the coatings which changed the developing
times. NO other differences as I understand. Generally
less time (1-2 minutes on average) is needed vs. the old
films but you should retest. Kodak's recommended times
are in their Tri-X pdf downloads:

Old Tri-X
http://www.kodak.com/global/en/professional/support/techPubs/f9/f9.pdf

New Tri-X
http://www.kodak.com/global/en/professional/support/techPubs/f4017/f4017.pdf

Help!  I've been using TriX for the best part of 50 years,
and tonight developed my first roll of 120 400TX.  I've
always used a pre-soak before the developer, but never
before have I seen a rich blue liquid come out of the tank
when emptying it.  Is there a water soluble blue dye on the
film now that was NEVER used before?  I rinsed the film 4-5
times, and the blue solution became more and more dilute.
Proceeding with the development routine, nothing else
unusual occurred--except maybe the film-base fog seemed a
bit heavier than usual.  Is this new film truly a radical
and surprising deviation from the past versions of Tri X?
Thanks for your help.

R.W. Behan

  I will be talking to a Kodak specialist tomorrow about
the changes in their films since moving B&W film into the
color film plant at Rochester. I think T-Max had already
been made there for some time but Tri-X and Plus-X were not
and have had some changes. Kodak notes in their press
releases that this includes better anti-static properties
which suggests a change in the overcoating and backcoating.
Its possible that the type of dye used for anti-halation was
changed. This dye is in the back coating which also serves
to compensate for curling of the film. Anti-halation dye is
generally made colorless by the sulfite in both developers
and fixing baths. So, while it may come out in a pre-soak it
may not show up by coloring the developer. The anti halation
dye is not always removed. One of the symptoms of the
decomposition of safety film base (so called Vinegar
syndrome due to the accompanying odor) is the regeneration
of the decolorized dyes resulting in colored splotches on
the film.
  Sensitizing dye is another matter. Sensitizing dyes are
used to make film sensitive to color, the basic silver
halide being sensitive only to blue and UV light. In some
films this dye is persistent, T-Max and Delta being
notorious for this. While the residual dye is often blamed
on insufficient fixing it is probably just very tightly
bound to the gelatin even when the film is completely fixed.
A treatment in a sodium sulfite wash aid, Kodak Hypo
Clearing Agent for instance, will remove this dye. It will
also decolorize any anti-halation dye that may remain.