I've read numerous posts asking variations of what is a User Theme, how to install a User Theme and how to select a User Theme. I'm requesting a forum moderator create a sticky post that answers the questions. I'm taking a stab at creating a sticky worthy post but I'm certainly open to alternatives.
What is a Theme? A theme is a graphic image and color container, or skin, that changes the looks of the Cakewalk by Bandlab user interface or UI. A theme does not change features or behavior, just how the program looks. Cakewalk by Bandlab has two Bandlab Technologies created themes, Mercury and Tungsten. All other themes are created by third parties and collectively named "user themes".
Theme files have the .sth file extension and are stored at c:\Cakewalk Content\Cakewalk Themes by default.
Select themes by pressing p on the computer keyboard, or navigate to Edit > Preferences to open the Preference window then Customization > Themes
Unless you are going to create or modify a theme, the theme editor available as an add-on selection in the Bandlab Assistant is not needed.