My guess is that anyone using Tableau and custom colors in the preference file has always suspected that there are more settings available. And in fact, that is the case. As an example, notice the color of the slider control and the map controls.
Please note, this is not supported by Tableau, but it works in the same way as the custom color palettes. There should be no issues with modifying this file, as you can simply remove this code and everything will default back to "normal" in Tableau. However, these settings will follow the workbook, so anyone opening the workbook will also have these settings. The preference file is loaded up front when opening Tableau and then saved with each workbook. So if you load the preference file with a pink slider control, then when it's saved, the pink slider will follow that TWB/TWBX file. The only way to change this after it's saved is to go into the workbook and delete the preference settings from the beginning of the workbook.
The Tableau Preference File should be located in your documents folder "...Documents\My Tableau Repository\Preferences.tps". Simply open this file in a text editor and add the lines of code to set the preferences. The code should be added within the preferences tags, either before or after your custom color palettes.
Below are some additional settings that can be added to the preference file to change various settings in Tableau.
This first list was posted by Russell Christopher on Github here.
After spelunking for more namespaces, here are some additional preferences that can be set in the Tableau Preference File.