I tried some V on some chrome I have around and it did not darken it, whereas, the instant it touches veg the veg goes black.
This is what I would do, take some water, wet a scrap thoroughly, then shake it off. If the surface seems damp at all then I think you can:
1)Take another scrap, dampen in tea, very strong tea. There are other things that do tanic acid even more strongly. But tea is a nice household thing.
2) Let one piece dry, and try the V on that, and try the V on the wet piece before it dries. Veg goes black because it has the tanic acid left over from the bark tan, or similar process. But you can dye something like cotton that does not, simply by first putting some tea on it. Now the problem with chrome is it does not wet out that well, but I think you can get past that.
Another option is to use black dye. Dean of all things holster, Will Ghormley, has a section on his site about dyeing with ecoflow.
http://www.willghormley-maker.com/OldDogsAndNewTricks.html