Answer 1

No. The games are specifically programmed such that Reshiram, Zekrom and Victini can never be shiny, when encountered in the game.

It's possible that in future events or games they could be shiny.

Comments

**The only way to get a shiny zekrom/reshiram is hacking, but your game might have problems after this hacking...

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You are absolutly right in your answer. I think there may be an event at some point because there ARE sprites for shiny versions of the Pokemon.