By default Sidenav will use your Theme colors that you have set inside of your Thinkific theme, but you can also either choose a preset theme or have complete control over all of the colors used.
Choosing a theme preset
Open up the Colors settings group of the Sidenav Menu section and choose a color scheme preset
Thinkific : will use the colors you have in your Theme Settings
Dark: will use a preset "dark theme" : you can also choose the "primary color" to use
Light: will use a preset "light theme" : you can also choose the "primary color" to use
Custom: will allow you to specify colors for all of the elements on the page (using the color selectors right below the dropdown)
Creating a custom color scheme
When you select a Custom option from the Color Scheme dropdown, the color sectors become active. Configure each color option to change the color for that specific element