What is Case greenbone?

[lithicus]

From Steve Pfeiffer's book, "Collecting Case Knives", he states:

For bone-handled knives, the values shown are for basic or “dark” bone handles or for handles with very minor coloring.
For Case XX stamped knives with “true” green bone handles, values will be...

Since the title of this thread is, "What is Case greenbone?" I personally would like to see some more comparisons of what is considered "basic or dark bone handles" vs "true green bone handles" as this is what is most confusing to myself. Here are a few examples I was able to find in this book. If this is a violation of any terms or copyrights or anything, I will promptly remove and apologize!!

Green bone to regular bone:

Dark black bone to green bone:

An example of "dark green bone" handles:

An example with "green bone" on the left and "dark (black) bone" on the right: