Board Thread:Show-Related Questions and Answers/@comment-5279400-20171228052950/@comment-25926288-20171228112644

I think Zelena’s envy just leaks into all magic she does. I think the silver slippers simply produces white smoke for those that are pretty much good natured.

I think along the lines of the Author’s quill. Isaac teleported away in purple smoke, yet when Henry teleported the crystal it was white.

The next closest attribution is pretty messy as the Holy Grail Power was red for dark people (Rumple and Hook), Grey for Emma, and purple for super pure Merlin.

Toss the last example aside, I think white smoke symbolizes light magic/the purity of heart.