Yes, it is an original color named "Deep Pink." I've seen only two-three cars in that color; yes, quite rare. I guess that it looks a little bit too much like a Barbie car or a Mary Kay Cosmetics color for most people.
By the way, I think that the owner is looking at Mark I (Bugeye) NADA values when he quotes an increase from $12,000 to $14,500. No square-bodied Sprites are selling in that range (except a couple of auction anomalies); only the Bugeye Sprites trade in that price/value range.