/usr/share/themes/Adwaita/gtk-3.0/settings.ini is in gnome-themes-standard-data 3.10.0-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | [Settings]
gtk-color-scheme = "base_color:#ffffff\nbg_color:#ededed\ntooltip_bg_color:#343434\nselected_bg_color:#4a90d9\ntext_color:#2e3436\nfg_color:#2e3436;\ntooltip_fg_color:#ffffff\nselected_fg_color:#ffffff"
gtk-auto-mnemonics = 1
gtk-visible-focus = automatic
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