Hi Erik Anderson,
Thank you for contacting us.
WinForms Theme Studio supports only the Office2019Colorful and HighContrastBlack themes, and no other prebuilt themes have been available for customization so far. For more information, please refer to the following documentation:
Theme Studio-Based Themes:
If you would like to use themes such as Office2016Colorful, Office2016DarkGray, or other built-in themes, you can apply them using the SkinManager.
Please refer to the following documentation for details:
Getting Started with SkinManager:
Please let us know if you need any additional information or further assistance.
Regards,
Yuvaraj M