I saw this thread and wanted to fill you guys in on the way this mod is done. This is not proprietary code or anything of the sort. It's simply an edited apk that somebody took the time to do and uploaded it. You should give credit to whomever actually did the edits and uploaded the files but otherwise this isn't really a "mod" in my opinion. What this is is a modified apk from a specific carriers device (SecSetting.apk, SystemUI.apk, etc) But before I go into detail on how to do this yourself quite easily, I think you all should know that flashing or "hot swapping" a system apk from a different device model can and WILL screw things up in your settings and more. It WILL break settings and features. You may not notice right away but if you start looking through all of your settings you will be missing things and some things will not work. Specifically any setting or feature that relies on csc, which is a lot of things.
First of all you must be rooted in order to modify system files. What you want to do is pull the correct SecSettings apk from your own device, stock rom tar, etc then modify the values to your liking. Decompile the apk with apktool or baksmali etc. (If you don't know what this is then you can stop reading as this is beyond the scope of the typical user). Navigate to res/values and you will see a short list of xml files. The easiest way to achieve the dark theme is to edit the default theme inside the styles.xml. This tells the phone which factory theme to use throughout the settings apk. Most of the font colors will automatically be changed with the theme. I learned this from reading a post a while back and although it wasn't in great detail, I quickly figured out the entire concept and re-themed my apk's in a few minutes then recompiled. I also learned on my own that the framework res contains all the references for the themes in the same values directory. If you're unsure of the correct theme name to type in the styles.xml, look in framework-res values folder (after you decompile it with apktool). Now I didn't go into great detail here because that's basically something for a whole new thread. I jst don't think somebody should start a thread like this using somebody else's modified work without their knowledge or permission. So that's that.
@op Don't snake somebody's work and fail to give them credit in your OP. You look like a fool when you do this. If anybody wants to try this mod themselves feel free to pm me. I can offer help if you have some basic decompiling/recompiling knowledge.