I used http://colorsublime.com/ - it took me about 1 second to install Afterglow.
Colorsublime installation instructions (using Package Control):
1. CMD ^ P
2. Type "install" and select "Package Control: Install Package"
3. Type "Colorsublime" and select "Colorsublime"
Installing the theme: 1. CMD ^ P
2. Type "theme" and select "Colorsublime: Install Theme"
3. Type "afterglow" and select "Afterglow"
Profit.When using Colorsublime (steps 1 + 2 of the second set), you can also arrow up and down through the themes and get a live preview of each as you do so.
Note: Colorsublime only installs the color scheme. If you want to take full advantage of a theme like this (includes custom tab styles, custom sidebar styles, etc.), you'll need to follow the directions on their website.