Well, that's the thing. Standard WW2 German military uniforms are not 'Nazi' uniforms. They're usually Wehrmacht (German regular army) or Luftwaffe (airforce).

SS and Waffen-SS uniforms are, however, decidedly Nazi. Originally, they were black. but later on the combat divisions wore grey. As I say, the trick is to check the collar tabs. The SS runes are a dead giveaway for Verfugungstruppe or Allgemeine SS. A skull and crossbones indicates Totenkopfsverbande while a key shows Liebstandarte-SS Adolf Hitler and a key crossed with the SS runes means Hitlerjugend Division. A flag or crest of a non-German country indicates Waffen-SS.

SS rank names are different. The Wehrmacht equivalent of Colonel is Oberst, but the SS version is Standartenfuhrer.

Given the atrocities carried out by the various SS units, it is unsurprising that the sight of the uniforms upsets people. I personally find the Britische Freikorps offensive because I'm still old-fashioned enough to dislike traitors.

I loved 'Allo 'Allo, but the only actual Nazi in the show was Herr Flick of the Gestapo. All the other Germans were Wehrmacht and not Nazis at all. General von Klinkerhoffen was still fightng for the Kaiser!