SPI orange is very vibrant as stated. I have not seen any factory color that resembles it. Put a factory orange next to Barry's orange and everyone will be drawn to the SPI car like a bug light. It is just stunning in the sunlight.... my Coronet in my avatar is SPI orange.
Can't say anything about GM but for Plymouth is the nothing like it. When I park next to Vitamin C or GoManGo nobody looks at the factory orange. This orange has lot more red in it I think. The factory orange is flat and lifeless compared to Barry's Orange as Barry can make it Orange.