Gnome 2.28 has around 21 Themes of various colors, mostly light and bright. Using your machine a lot or late into the night, a light or bright colored theme is tiring for the eyes. Gnome's darker themes are Unity, Amaranth and Darklooks.
Unity and Amaranth are acceptable but too light. Darklooks is dark enough but color wise its awful. Its way too "brown".
Adjusting it to a more acceptable hue, ie strip out the brown, I did this:
Windows Background: #474A56
Windows Text: #E6E6E6
Input Boxes Background: #6C6F7F
Input Boxes Text: #D3D7CF
Selected Items Background: #31353D
Selected Items Text: #7AA3CC
Tooltips Background: #EDDE5C
Tooltips Text: #000000
I posted these settings mainly for my own reference. Your welcome to try them if your so moved.