Tangerine is an alternative theme for the main Mastodon web interface.
To enable Tangerine on your vmst.io account, visit Preferences > Appearance > Site Theme > Tangerine.Enable Tangerine
Unlike other theme options, it will automatically switch between dark and light mode based on your system settings. There are also a Cherry variant, and for folks who like the layout options of Tangerine, but prefer a the stock Mastodon color scheme, there is also a purple option.
To disable Tangerine, select one of the default Mastodon themes from the same control panel option.