This is an alternative version of the Adwaita GTK theme (default in Gnome Shell). The dark vesion has fully neutral grey colors, instead of the green hues in the original.
The main reason for making this was using the dark theme with gThumb and MyPaint (and maybe Inkscape and GIMP in the future too!). The green hues of the original can affect the way you percieve hues in the image/video you're working on. For design work it's advisable to use neutral greys in the UI.
(It also looks way cooler)
Read more about color theory: on Wikipedia
The light version is not changed. Based on 3.16.
