Board Thread:General Discussion/@comment-26944197-20150903060408/@comment-1031724-20161029061139

I wondered which would be which. My guess was the Soul Stone would be orange because "soul" and "spirit" are sometimes synonymous and the Spirit element is orange in Legend of Zelda: The Wind Waker.

I was also sure the green one would be revealed next because they seem to alternate between "cool" and "warm" colors (blue, red, purple, yellow), plus orange always seems to be last, as it's the rarest color along with purple, though the purple one was revealed third.

And, we now know the green one is the Time Stone.