As requested, I will take all the evidence we have both Canon and Legends to hypothesize where Luke got his crystal for his lightsaber. Since Canon now says lightsaber crystals are all the same and merely change due to the user's intentions/force powers, then we can't say the crystal was green to begin with, however we can analyze whether or not the Kyber Crystal has been used from Qui-Gon Jinn's or not.
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