Hisuian Zoroark is supposed to copy the image entirely of the last last pokemon in the party, even if that pokemon is shiny, but I found while playing on Limitless MC that Zoroark does not copy the shiny form. If it takes the image of, say, a shiny Yveltal, it will appear in sprite as a normal Yveltal and a shiny in body, making it obvious that the pokemon is a Zoroark. I suspect that this applies to any alter form but haven't had the chance to test it.
It should be replicable by just getting a shiny and a hisuian Zoroark.l and entering a battle.