This color scheme uses the same colors from the SSMS One Dark Theme I posted, it is just slightly different as pgAdmin does not have all of the same syntax highlighting options as SSMS. (Imagine that) For those interested I created this theme on a Windows 10 machine running pgAdminIII version 1.20.
You can install this theme by importing the following registry file.Download pgAdmin One Dark Theme
I also updated the font to Consolas size 11 and added line numbers. For those settings you can change them manually in the pgAdmin > File > Options> Query tool > Query editor settings menu or alternatively you may also import the following registry file.Download pgAdmin Custom Font Settings