Specifically going from what you gave us... the photo you posted.
There are a total of 5 "differences" and they are as follows...
One black mod and one silver mod.
The black tank on the left has ORANGE o-rings.
The black tank betweeen the two mods has GREEN o-rings.
The airflow on the black D20 mod is WIDE OPEN.
The airflow on the silver D20 mod is CLOSED.
The color I prefer is not shown in the PHOTO... I prefer the BLUE one.
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