/usr/share/themes/Green-Submarine/gtk-3.0/settings.ini is in mate-themes 3.22.16-4ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | [Settings]
gtk-color-scheme = "base_color:#FFF\nbg_color:#CBD9D4\ntooltip_bg_color:#DBFFF3\nselected_bg_color:#72B49D\ntext_color:#1A1A1A\nfg_color:#101010;\ntooltip_fg_color:#000000\nselected_fg_color:#ffffff\nlink_color:#00CC85\nbg_color_dark:#1F2724\nfg_color_dark:#E6E6E6"
gtk-auto-mnemonics = 1
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