Copper oxides go from bright aqua blue to dark blue to brownish to dark brown to pink. All dependent on the amount of oxygen, other oxidizers and metal ions present. The pink is most common in cartridge brass, but it is not only coloration that signals dezincification. If 50% or less of the zinc is removed, you might not get any color change at all, just the dull appearance.
What you have shown is the the copper oxide on the surface is removed (expected)as the acid concentration increases and that the dezincification has moved deeper into the case. In most of the cases I have worked on where dezincification has fully penetrated and resulted in fracture, the surface looks brassy and dull with a light pink or brown tint. The pinkish layer, in some cases, is deep into the structure. I know it is fun to try and beat a subject matter expert, so you can go with your test if you want. But what you proved is that you have over annealed and burned off zinc leaving a ruby red color. Sure, that copper oxide will be easily removed, but that does not mean the zinc has not been removed, in fact, in that case it was removed by flare off and acidic attack.