I have to weigh in on this one! It is my opinion (I may be wrong since I do not have the marble in hand) this is not authentic. first of all there are no cut lines. second, you really don't see a pure opaque red on guineas. most of the red is a blend of electric orange. The yellows are a little too intense. We all would like a green based guinea but you cannot become irrational.
The odds of finding a blue ray, red devil, blue devil or green based guinea in the wild are astronomical. I mean how often do you find common guineas, three color flames and transparents?