/usr/share/themes/BlueMenta/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 4 | [Settings]
gtk-color-scheme = "base_color:#f7f7f7\nbg_color:#d4d4d4\ntooltip_bg_color:#F5F5B5\nselected_bg_color:#6699CC\ntext_color:#2c2c2c\nfg_color:#2c2c2c;\ntooltip_fg_color:#2c2c2c\nselected_fg_color:#ffffff"
gtk-auto-mnemonics = 1
gtk-visible-focus = automatic
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