BUG: Online workbench doesn't reflect the theme colors of the parent web properly
There is a bug in the Online Workbench that you are not able to test theming on your web parts when the following two themes will be used:
* Dark Yellow
* Dark Blue
As documented in the Issue on GitHub https://github.com/SharePoint/sp-dev-docs/issues/1064
This would be really beneficial for testing web parts and how they look like when different themes will be used.