/usr/share/themes/Shiny/gtk-3.0/settings.ini is in mate-themes 1.9.2-1.
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:#ffffff\nbg_color:#efebe7\ntooltip_bg_color:#f5f5b5\nselected_bg_color:#FFBE6B\ntext_color:#1a1a1a\nfg_color:#101010\ntooltip_fg_color:#1a1a1a\nselected_fg_color:#1a1a1a\nlink_color:#DD4814\nbg_color_dark:#efebe7\nfg_color_dark:#1a1a1a"
gtk-auto-mnemonics = 1
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