I am certain that Rey is a grey Jedi. the Jedi have flaws with their philosophes, when Luke taught Rey on Ahch-To, the lessons were all about highlighting those flaws. During the first one in particular, while Rey is meditating on the rock, she essentially learns a balance between light and dark is necessary. Between everything from life to death, peace to violence is the Force that binds it all together. The Force does not belong to the Jedi (or the Sith, for that matter) and just because they no longer exist doesn't mean the light has completely vanished. It's natural to take bits and pieces from both sides; one of the Jedi's shortcomings was their complete suppression of emotions, but it was Luke's love for his father that brought Anakin back to the light. Redemption never occurred to Yoda or Obi-Wan, who withheld the truth from Luke as they trained him in the Jedi ways.