I have this navigation tool bar at the bottom of my screen and I can't figure out how to change the backfround of it to light grey. Any advice?

          // Bottom Navigation
                    ToolbarItemGroup(placement: .bottomBar) {

                        Button(action: {
                            print("mob: Performance tapped")
                        }, label: {
                           Label("Performance", systemImage: "chart.line.uptrend.xyaxis")
                               .labelStyle(VerticalLabelStyle())
                               .frame(maxWidth: .infinity)
                        })
                        Spacer()

                        Button(action: {
                            print("mob: Funnel tapped")
                            showFunnel = true
                        }, label: {
                           Label("Funnel", systemImage: "arrowtriangle.down.fill")
                              .labelStyle(VerticalLabelStyle())
                              .frame(maxWidth: .infinity)
                        })
                        Spacer()

                        Button(action: {
                            print("mob: AB tapped")
                            showAB = true

                        }, label: {
                           Label("AB", systemImage: "list.bullet.rectangle.fill")
                               .labelStyle(VerticalLabelStyle())
                               .frame(maxWidth: .infinity)
                        })
                        Spacer()

                        Button(action: {
                            print("mob: KW tapped")
                            showKW = true

                        }, label: {
                           Label("KW", systemImage: "text.alignleft")
                              .labelStyle(VerticalLabelStyle())
                        })
                    }

this is a very good question, i have struggled with this as well, some have suggested to use

init() {
UITabBar.appearance().backgroundColor = UIColor.red
}

but they are more like UIKIT based and also do not work in all cases, i wll look for a answer to this one for sure

Thank you for responding Amit. Sadly this didn't work. I see where you are coming from. I used an init to modify the top toolbar and that work, see below. But I cant seem to get the bottom nav bar changed.

    init() {
      let coloredAppearance = UINavigationBarAppearance()
      coloredAppearance.configureWithOpaqueBackground()
      coloredAppearance.backgroundColor = .systemGray4
      coloredAppearance.titleTextAttributes = [.foregroundColor: UIColor.white]
      coloredAppearance.largeTitleTextAttributes = [.foregroundColor: UIColor.systemGray]
      UINavigationBar.appearance().standardAppearance = coloredAppearance
      UINavigationBar.appearance().compactAppearance = coloredAppearance
      UINavigationBar.appearance().scrollEdgeAppearance = coloredAppearance
      UINavigationBar.appearance().tintColor = .white
    } 

This compiles but does not work

    init() {
        let tabBarAppearance: UITabBarAppearance = UITabBarAppearance()
        tabBarAppearance.backgroundColor = .systemRed
    }

Try this

struct ContentView: View {
    var body: some View {
        TabView {
            Text("Home")
                .tabItem {
                    Label("Home", systemImage: "house")
                }
            Text("Search")
                .tabItem {
                    Label("Search", systemImage: "magnifyingglass")
                }
            Text("Notification")
                .tabItem {
                    Label("Notification", systemImage: "bell")
                }
            Text("Settings")
                .tabItem {
                    Label("Settings", systemImage: "gearshape")
                }
        }
        .tint(.white) // <- change the color of each tab icon
        .onAppear {
            let tabBarAppearance = UITabBarAppearance()
            tabBarAppearance.backgroundColor = .red
            UITabBar.appearance().scrollEdgeAppearance = tabBarAppearance
        }
    }
}

I have been looking at sarunw blog How to change TabView color in SwiftUI and this should work in iOS16 but it did not for me. maybe a bug.

struct ContentView: View {
    var body: some View {
        TabView {
            Group {
                Text("Home")
                    .tabItem {
                        Label("Home", systemImage: "house")
                    }
                Text("Search")
                    .tabItem {
                        Label("Search", systemImage: "magnifyingglass")
                    }
                Text("Notification")
                    .tabItem {
                        Label("Notification", systemImage: "bell")
                    }
                Text("Settings")
                    .tabItem {
                        Label("Settings", systemImage: "gearshape")
                    }
            }
            .toolbar(.visible, for: .tabBar)
            .toolbarBackground(Color.yellow, for: .tabBar)
        }
    }
}