How can I change default dialog button text color in android 5

I have many alert dialogs in my app. It is a default layout but I am adding positive and negative buttons to the dialog. So the buttons get the default text color of Android 5 (green). I tried to changed it without success. Any idea how to change that text color?

My Custom dialog:

public class MyCustomDialog extends AlertDialog.Builder {

    public MyCustomDialog(Context context,String title,String message) {
        super(context);

        LayoutInflater inflater = (LayoutInflater) context.getSystemService( Context.LAYOUT_INFLATER_SERVICE );
        View viewDialog = inflater.inflate(R.layout.dialog_simple, null, false);

        TextView titleTextView = (TextView)viewDialog.findViewById(R.id.title);
        titleTextView.setText(title);
        TextView messageTextView = (TextView)viewDialog.findViewById(R.id.message);
        messageTextView.setText(message);

        this.setCancelable(false);

        this.setView(viewDialog);

    } }

Creating the dialog:

MyCustomDialog builder = new MyCustomDialog(getActivity(), "Try Again", errorMessage);
builder.setNegativeButton("OK", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialogInterface, int i) {
                            ...
                        }
}).show();

That negativeButton is a default dialog button and takes the default green color from Android 5 Lollipop.

Many thanks