The 504th shipped over to Tunisia 11 Tigers and 19 PZIIIs. There are pictures of a PZIII J attributed to the 504th in Sicily but in Tunisia the unit would have had the Ausf Ns as they were the support model to protect the Tigers from enemy infantry and flank attacks.

Both the 501st and 504th were part of Von Arnim's 5th Panzer Armee and generally under the command of the 10th Panzer Division.

The 501st was absorbed into the 7th and 8th Kompanies of Panzer Regiment 7 on 26 February where they served alongside Panzer IV Gs. On 17 March the remnants of the 501st were attached to the 504th until they surrendered in May. We do not know if this included any remaining PZIIIs or PZIVs at the end.

Colors in use at the time reflect the orders of the day, you can safely paint your tank in all RAL8000, RAL7008, or 2/3 RAL 8000 with 1/3 RAL 7008 as the disruptive pattern. You can also paint it RAL8020 with RAL 7027 as the disruptive pattern.

Now if you're going to depict a PZIV F or older or PZIII J or older you would use Dunkelgrau for the 1940 and early '41 vintage tanks and RAL8000 for the rest. You can also paint them Dunkelgrau covered with mud, or Dunkelgrau covered lightly with RAL8000. I'm sure some were painted with 7008 too!

Here's a pic of 2 of my Tunisian Panzers in 8020/7027: