SwiftUI: how to change NavigationView.toolbar background color

Solution 1:

You can do this using UIToolbar appearance. Tested with Xcode 12 / iOS 14.

struct DemoView: View {
    
    init() {
        UIToolbar.appearance().barTintColor = UIColor.red
    }
    
    var body: some View {
        NavigationView {
            List {
                Text("Item")
            }
            .toolbar {
                ToolbarItem(placement: .bottomBar) {
                    Button(action: { }, label: {Text("ITEM1")})
                }
                ToolbarItem(placement: .bottomBar) {
                    Button(action: { }, label: {Text("ITEM2")})
                }
                ToolbarItem(placement: .bottomBar) {
                    Button(action: { }, label: {Text("ITEM3")})
                }
            }
        }
    }
}