SSMS 2016 Dark Theme

I used this approach and theme provided here, it worked for me in SSMS 2008:

Beautify Your Management Studio 2005/2008

To install, simply backup your [HKEY_CURRENT_USER\Software\Microsoft\Microsoft SQL Server\100\Tools\Shell\FontAndColors{A27B4E24-A735-4D1D-B8E7-9716E1E3D8E0}] registry key, and load in this new set (standard disclaimer about being careful with your registry, make sure you know what you’re doing, don’t blame me, etc). You can then either restart SSMS, or go to the Tools, Options, Environements, Fonts and Colors and simply click OK.

There is also a comment which provides the proper registry location for changing the theme in SSMS 2012, which only seems to differ by the version number.

Variable colors share settings with table, object and other names. So you can change the text color using Identifier:

Just note that it will also affect table names, column names etc.

For the highlighted color of identifiers and variables, use Selected Text. The highlights will use a slightly muted version of that color.

And no, these are not my current settings, and I only kept them that way long enough to grab a screen shot...