I thought it to be thier position to the Great Journey: Moriquendi (mori
literally meaning black) being elves who did not see the Two Trees, though usually assumed for Avari, could be Black. The High Elves, Caliquendi, (Light approx. White), saw the Light of the Trees, and made it to Valinor. The Grey-Elves were those that accepted the Journey, but did not go directly to Valinor, (the Sindar, elves under Thingol
Greymantle)
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Lincoln continental mark v