Board Thread:Spoilers!/@comment-27060727-20170218051023/@comment-25375217-20170425163812

FrancisPaul wrote: We know that Fiona had a color before black and it's one of the colors of the rainbow.

I'm inclined to believe she was the Blue Fairy, and Reul Ghorn sent her away to replace her. I think Kat already confirmed that's not the case. And she heavily implied it would be yellow.