As far as glass quality is concered. Starphire has become a term for any kind of low-iron glass, where as there are number of different glass formulations that are low-iron.
It seems to me that "Edge Color Guide" actually refers to the Opto-clear or Opto-white glass, which have almost no tint at all because all impurities were removed not just iron.
The best way I have been told to differentiate between regular glass and starphire is by the tint color of the edge, Starphire glass is supposed to be more blue (like the color of sapphire) where as regular glass is greenish. My SCA 150g edges have a distinctly blue tint.
I believe due to the presence of blue tint to the glass, SCA correctly refers to their glass as Starphire (sapphire).
If you are looking at the tank under a warm (yellow) light, blue starphire glass would appear more green.