GOKAAAAI... SILVER!
Reshiram and Zekrom were also hardcoded in the Gen V games to never be Shiny, but in ORAS and other later games where they’re catchable this is no longer the case. (They also had their catch rate changed to the standard Legendary catch rate of 3 in later games, since they had a slightly higher catch rate in Gen V because of being required to be caught as part of the story)