Yes, the leather colour (belt, cross-strap) for HJ was changed from
brown to black in 1937. The colour of HJ shorts went from
brown to black in the same year.
A reproduction HJ uniform ensemble would be pretty hard to put together I would have thought. Not the technical details (what insignia goes where, which strap to which sleeve triangle etc as we can help with all of that) but rather sourcing all of the items. We have had discussions in the past about reenacting and reproduction items but my impression back then was that it would be extremely difficult to put together a complete HJ uniform using only modern copies. Is that still true today?