RECOMMENDED: StartUI is a Bootstrap 4 Admin Dashboard Template which comes with both admin & frontend templates so you can build your whole site with it. Colour management is made easy with LESS files included and it claims 500+ different components included and multiple page layouts.
First Look Bootstrap 4 Themes - part 1
It's been a long time coming and we're still awaiting for the official release of Bootstrap 4 but that hasn't stopped some developers building these lovely Bootstrap 4 themes. Part 2 is coming soon.