In Slide Music WordPress Theme, all the menu related color settings are implemented in the WordPress Customizer area. To change the menu colors, please navigate to Appearance – Customize (or simply click on the Customize link from the WordPress admin bar), then choose Menu Colors option. You can change the colors for the menu bar, top level menu items, sub-menu items, mobile menu and all the colors that are used in the top menu area.
Please check the below video for better understanding.