ColorView+ContentView.swift

struct ColorView: View {
    @Binding var colorRectangleIsGreen: Bool
    var body: some View {
        RoundedRectangle(cornerRadius: 5)
        .fill(colorRectangleIsGreen ? Color.green : Color.blue)
        .frame(width: 100, height: 100)
        .padding()
    }
}

struct ContentView: View {
    @State var rectangleIsGreen = false
    var body: some View {
        VStack {
            ColorView(colorRectangleIsGreen: $rectangleIsGreen)
            
            Button(action: {
                self.rectangleIsGreen.toggle()
            }) {
                Text("Toggle color!")
            }
        }
    }
}