7.65mm Luger - Swiss, blue aluminum case - Proof?

I recently turned up a 7.65mm Luger of Swiss WW2 vintage, from when they were semi-experimentally making aluminum cases. This one is headstamped “M 3 T 44” and has a blue aluminum case, with “24” in what looks like mechanically-printed black in on the case side. Flat brass primer which is unfortunately snapped, plus a standard CNCS FMJ bullet.

Somewhere, back in a dim recess of what passes for the Wombat memory, I believe I read that the blue case indicates a proof load. Can anyone verify?

Once upon a time Jack Brickell sold me a fired empty such as you describe, identifying it as a proof case. I’ve assumed his ID was correct. JG

Your 7.65 Para from Switzerland, with blue-anodized aluminum case, is a proof load. It was loaded at the Eidgen