Hello Kealauluwe,
Follow the steps given below to change the Menus color
Go to Customizer –> General Configuration –> Header Settings –> Header Menu color, Header Current(Active) Menu color.

To change all menus box background color, follow the steps below
Go to Customizer –> General Configuration –> Header Settings –> Navigation Box background color.

Here is the theme complete documentation link below.
https://www.luzukdemo.com/docs/nirman-construction/
Thank You.