For clarification's sake, you only want the background of the name frame colored, you don't want anything else present in the screenshots? (For example the class icon instead of character portrait on that target frame in the second SS?)
There are plenty of addons that include the name background coloring, but also have a ton of other tweaks and features (though IDK if they're still working, I don't care for the default UF's myself and use SUF on live).
If all you want is the name background colored for certain units,
I can upload that right now, as I had done that for beta.
If you wanted a ton of other options, you could try something like UnitFramesImproved or Sennetta's Custom Script UI or one of the other addons that include that.
As for the particular addon that the screenshot is likely of, I think it's a modified version of
Santa UI(specifically
Santa UI Textures ), that's why the outlines of the unit frames are darker, in case you were wondering.
Edit:
File uploaded and likely approved at any moment. Fabulous mods are fabulous.
Here it is if you want it.