Shiny or not shiny?

[Nekra]

When a Pokémon with the Illusion ability switches into battle, it takes the form of the Pokémon in the last slot of the player's party.

So I think if the last pokemon in a party is not shiny, it is ok Dramsama masks self as nonshiny ('copy last pokemon's appearence').

You got the point, I agree it was not ok you encountered. In my opinion solution should be to hide a shiny mark during Dramsama's illusion (in opponent's side) - opponent shouldn't know, it is a shiny until unmasked.
In reverse case (regular Dramsama masking self as a shiny pokemon) should work it in similar way.

The first picture looks like it's hacked, although it is not true.