Null Reference Exception while programming Tic Tac Toe in WinForms - Can´t find the reason

Question

My plan was to have a field of 3*3 with buttons and change the color (which is used to mark a button) by every turn. So i created a playerclass in which the color of the player should be stored and used this string to check, which color should be used in form1. Problem: Null reference exception in the method colorChoice. This is the code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace TicTacToe
{
    static class Program
    {
        /// <summary>
        ///  The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.SetHighDpiMode(HighDpiMode.SystemAware);
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace TicTacToe
{
    public class Player
    {

        public String playerColor = "Red";
        public int[,] storage;

        public Player(String playerColor)
        {
            this.playerColor = playerColor;
        }

    }
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace TicTacToe
{
    public partial class Form1 : Form
    {

        public static Player player1;
        public static Player player2;
        public static  Player currentPlayer;
        public Form1()
        {
            InitializeComponent();
            Player player1 = new Player("Red");
            Player player2 = new Player("Blue");
            currentPlayer = player1;
        }

        private void button1_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button1);
        }

        private void button2_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button2);
        }

        private void button3_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button3);
        }

        private void button4_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button4);
        }

        private void button5_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button5);
        }

        private void button6_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button6);
        }

        private void button7_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button7);
        }

        private void button8_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button8);
        }

        private void button9_Click(object sender, EventArgs e)
        {
            playerSwitch();
            colorChoice(button9);
        }

        private void colorChoice(Button button)
        {
            if(currentPlayer.playerColor == "Red") button.BackColor = Color.Red;
            if (currentPlayer.playerColor == "Blue") button.BackColor = Color.Blue;
        }

        public static void playerSwitch()
        {
            if (currentPlayer == player1)
            {
                currentPlayer = player2;
            }
            else //if (currentPlayer == player2)
            {
                currentPlayer = player1;
            }
        }
    }
}