How do I change the Next and Previous button color on units?

To change the color of the Previous and Next buttons:

First you can use the Customizer.

1. Click on WP Courseware→Settings.
2. Click on the Style tab.
3. Click the Yes radio button for Customize Colors.
4. Click the Unit Colors menu item on the left.
5. Modify any of the colors for the Unit Prev/Next Button.

You could also click the Use Customizer button and edit the same properties via the frontend customizer.