This series has five formats. http://henryaltemus.com/series/series121.htm

The third format has been seen in brown and purple previously. Now a green cover has been discovered. This format comes with a dust jacket that matches the book cover. The three cover colors are shown below.

In Series #166 Slip-in-the-Pocket Classics the Format 5 cover is identical to this book. That format has been seen in brown, blue and green.
The Series #166 books are boxed not jacketed. See: http://henryaltemus.com/series/series166.htm