The GTK2 theme is nearly identical to Mist-Redmond, except for the different theme color (green instead of blue).
The GTK3 window decoration style is designed to resemble the Xfce “Wallis” window decoration theme.
For debugging purposes, the default style for unkown elements in the GTK3 theme is strikingly colorful (yellow-magenta with thick red border). If you encounter elements with this style, please send a bug report to the author with your GTK+ version, the application, the element that shows the bug, and preferably a screenshot. (To find out your current GTK+ version, run
gtk3-widget-factory and check the “About Widget Factory” dialog from the menu in the upper right corner.)
For Arch Linux, the AUR package gtk-theme-mist-redmond-green is available.