I know this must seem basic but I can't get it to work. I want a button to change color when tapped but start grey, turn green on first tap then red on second tap and back to grey on third. I thought .background(Color.array[number]) in a foreach loop would do it but apparently not. Eventually I want to store the state of the button, so I don't think toggle would work.

Firstly it a very good question, so do not be worried about asking thing on this forum.

I have done this which works but not sure if it what you are looking for:

Make a struct (I usually put it in a file)

struct ChangeColorButton: ButtonStyle {
    let colors: [Color] = [.gray, .green, .red]
    let number: Int

    func makeBody(configuration: Configuration) -> some View {
        configuration.label
            .padding()
            .background(colors[number])
    }
}

then where you want to to place the button

struct ContentView: View {
    @AppStorage("buttonstatus") var number: Int = 0 // This store the color of button

    var body: some View {
        Button("Change Color") {
            changeColor()
        }
        .buttonStyle(ChangeColorButton(number: number))
    }

    func changeColor() {
        if number == 2 {
            number = 0
        } else {
            number += 1
        }
    }
}

Thank you so much, works perfectly!