What is the best way to implement Singleton pattern combined with Factory pattern in Java? Detail in description

I am learning design patterns for JAVA. I wanted to use factory pattern with singleton. Now I am not sure If I went with correct approach or not.

Let me share what I have tried first. I have used Button as example class. Aim is to get singleInstance of Button and then get it's color. Can anyone let me know if it's usable in actual implementation? Am I missing on anything or on a better approach?

Here's my code:

Button.java

public abstract class Button {
    abstract void getButton();
}

ButtonClientClass.java

public class ButtonClientClass {
public static void main(String[] args){
    Button red = ButtonFactory.getButton("RedButton");
    red.getButton();
    System.out.println("hashcode"+red.hashCode());
    Button red2 = ButtonFactory.getButton("RedButton");
    System.out.println("hashcode"+red2.hashCode());

    Button green = ButtonFactory.getButton("GreenButton");
    green.getButton();
    System.out.println("hashcode"+green.hashCode());
    Button green2= ButtonFactory.getButton("GreenButton");
    System.out.println("hashcode"+green2.hashCode());
}
}

ButtonFactory.java

public class ButtonFactory {
public static Button getButton(String button){
    if(button.equals("RedButton")){
        return RedButton.getSingleRedButton();      
    }else{
        return GreenButton.getSingleGreenButton();
    }
}
}

GreenButton.java

public class GreenButton extends Button{

    private static class GreenButtonHolder {
        public static GreenButton INSTANCE = new GreenButton();
    }
    private GreenButton(){}
    public static GreenButton getSingleGreenButton(){
        return GreenButtonHolder.INSTANCE;
    }
    @Override
    void getButton() {
    System.out.println("You have a GreenButton");   
    }
}

RedButton.java

public class RedButton extends Button{
    private static class RedButtonHolder{
        public static RedButton INSTANCE = new RedButton();
    }
    private RedButton(){ }
    public static RedButton getSingleRedButton(){
        return RedButtonHolder.INSTANCE;
    }
    @Override
    void getButton() {
        System.out.println("You have a RedButton"); 
    }
}