By 1944, uniforms were mixed and matched in endless combinations, including gobs of German uniforms cut from Italian camo... The greys though would be more likely Heer feldgrau (Field Grey) and SS Mausgrau (Mouse Grey) if you wanted to mix 'em that way... The important part is the jacket though.. Heer units would retain the Feldgrau blouse, Waffen-SS, the Mausgrau.. Panzergrau would only be used on the Stalhelm...
As for Waffenfarben here's my general guideline for SPGs and StuGs..
Heer units equipped with the Sturmgeschütz III (and later Sturmgeschütz IV) were:
Sturmgeschütz-Abteilung (later Brigade). Red.
Sturmgeschütz assigned to a Panzer-Regiment (beginning in May, 1943). Rose pink (exception III./Panzer-Rgt. 24. Golden yellow branch color).
Sturmgeschütz assigned to a Panzer or Panzerjäger-Abteilung. Rose pink.
Clear as mud, right?
So... Given that you're modeling a recon element's track, I'd go with EITHER: Red or Yellow, with Red being the first choice, unless you're going to get more specific about the unit, in which case the Yellow of the Cav would be the choice to make...
For instance: In the fall of 1944, a division was recovering from the very heavy fighting in France and the uniforms of the Panzergrenadier regiments were in very poor condition. During the withdrawal from France, an enterprising supply officer located a depot of Sturmartillerie uniforms with Totenkopf collar tabs piped in golden yellow. These uniforms were issued to Panzergrenadier-Lehr-Regiment 901 to replace their worn-out uniforms.
BTW, I'm pretty sure your guy is a Tamiya figure, from the 1970's German Tank Crew figure set, which showed a Panzer Black field blouse over Mausgrau trousers, since the figures were Waffen-SS Panzertruppen.. As for stripping the paint, I'm always leary about that, so I won't suggest anything, but I've read that oven cleaner would work...