KeyColorPreferenceKey.swift

✅ struct KeyColorPreferenceKey: PreferenceKey {
    
    static var defaultValue: Color = .white
    
    static func reduce(value: inout Color, nextValue: () -> Color) {
        value = nextValue()
    }
}

struct ContentView: View {
    
    @State private var keyColor = Color.white
    
    var body: some View {
        VStack {
            SettingsView()
        }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
        .background(keyColor)
        ✅ .onPreferenceChange(KeyColorPreferenceKey.self) {
            keyColor = $0
        }
    }
}

struct SettingsView: View {
    
    var body: some View {
        ScreenSettingsView()
    }
}

struct ScreenSettingsView: View {
    
    var body: some View {
        KeyColorSettingsView()
    }
}

struct KeyColorSettingsView: View {
    
    @State private var color: Color = .white
    
    var body: some View {
        VStack {
            Button(
                action: {
                    color = .yellow
                },
                label: {
                    Text("YELLOW")
                }
            )
            
            Button(
                action: {
                    color = .red
                },
                label: {
                    Text("RED")
                }
            )
        }
        ✅ .preference(key: KeyColorPreferenceKey.self, value: color)
    }
}