Kethis, the Hidden Hand
Oracle Text
Legendary Spells you cast cost
less to cast.Exile two legendary cards from your graveyard: Until end of turn, each legendary card in your graveyard gains "You may play this card from your graveyard."
Legendary Spells you cast cost
less to cast.Exile two legendary cards from your graveyard: Until end of turn, each legendary card in your graveyard gains "You may play this card from your graveyard."
The effect says the cards in your graveyard gain that text. So it only applies that text once to cards that are there, and once the Amber moves zones, it becomes a new entity and loses that text.
If Kethis simply read "Exile two legendary cards from your graveyard: You may play legendary cards from your graveyard this turn.", then your shenanigans would fly, but I think Wizards carefully worded it for that reason.
If for some new setting they decided to have elves still be green mana but largely dark-skinned like this guy, similar to how the humans of the Zhalfir are dark-skinned, I bet some minority of MTG players would flip their absolute shiz.