Brand Colors add-on add more than 50 color options to your Brand WordPress theme.
First of all make sure you have installed Brand Premium plugin and have activated Brand Colors in Settings > Brand Premium > Add-ons.
Now, to find your color options go to Appearance > Customizer. Here you can find the Colors panel.
Now, just navigate to the section where you want to change the colors, click on Select Color and choose your color.
Navigation colors section has a background opacity extra option.