If your theme has a dark background, you'll find it much easier to work with Hypervisual if you change two settings inside the app.
First, open Hypervisual Settings (Tools > Hypervisual Settings, or use the Settings button on your Hypervisual dashboard):
Change the Theme background color to black (or your theme's background color -- this doesn't need to be exact as it's only for your ease of use in the editor). Then change the Default text color to white.
Click Save Changes, and you're done. Now when you add sections to your Hypervisual pages they will have white text by default, and you'll see them contrasted against your dark background inside the editor.