What color is the stone in Aragorn's ring?

yep, you better believe it. green it is :)

Green. It's emeralds.

“(…)green jewels gleamed there that the Noldor had devised in Valinor. For this ring was like to twin serpents, whose eyes were emeralds, and their heads met beneath a crown of golden flowers, that the one upheld and the other devoured; that was the badge of Finarfin and his house.” (Silmarillion)''

Es verde. Y en el primer libro cuando Glorfindel esta buscando a Aragorn y a los hobbits, le deja cerca de un puente una señal que Aragorn nombra "piedra de elfo" que creo es verde también (porque es como su símbolo).

Esmeralda Green XD