Try & Error

[DllImport("user32.dll")]

static extern IntPtr GetDC(IntPtr hWnd);

[DllImport("user32.dll")]

static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

[DllImport("gdi32.dll")]

static extern int GetPixel(IntPtr hDC, int x, int y);

//GetPixel()함수 정의, Color객체 반환

static public Color GetPixel(Control control, int x, int y)

{

Color color = Color.Empty;

if (control != null)

{

IntPtr hDC = GetDC(control.Handle);

int colorRef = GetPixel(hDC, x, y);

color = Color.FromArgb(

  (int)(colorRef & 0x000000FF),

  (int)(colorRef & 0x0000FF00) >> 8,

  (int)(colorRef & 0x00FF0000) >> 16);

ReleaseDC(control.Handle, hDC);

}

return color;

}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Text.RegularExpressions;


namespace Color_tool
{
public partial class Form1 : Form
{
    Regex rgbInputR;
    Regex rgbInputG;
    Regex rgbInputB;

    Match R, G, B;
    int r;
    int g;
    int b;


    string colorX;

    [DllImport("gdi32")]
    private static extern int GetPixel(IntPtr hdc, int x, int y);
    [DllImport("User32")]
    private static extern IntPtr GetWindowDC(IntPtr hwnd);

    private static readonly IntPtr DesktopDC = GetWindowDC(IntPtr.Zero);

    public static System.Drawing.Color GetPixelAtCursor()
    {
        System.Drawing.Point p = Cursor.Position;
        return System.Drawing.Color.FromArgb(GetPixel(DesktopDC, p.X, p.Y));
    }

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        button1.BackColor = Color.Black;
    }

    private void timer1_Tick(object sender, EventArgs e)
    {
        colorX = GetPixelAtCursor().ToString();
        Color backX = GetPixelAtCursor();
        this.BackColor = Color.FromArgb(r,g,b);
        label1.Text = colorX;
        RGB_value();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        if (timer1.Enabled == false)
            timer1.Enabled = true;
        else
            timer1.Enabled = false;
    }

    private void RGB_value()
    {
        rgbInputR = new Regex(@"(?<=R=)\d{0,3}");
        rgbInputG = new Regex(@"(?<=G=)\d{0,3}");
        rgbInputB = new Regex(@"(?<=B=)\d{0,3}");

        Match R, G, B;

        R = rgbInputR.Match(colorX);
        G = rgbInputG.Match(colorX);
        B = rgbInputB.Match(colorX);
        //had to flip the R and B ???
        b = int.Parse(R.Groups[0].Value);
        g = int.Parse(G.Groups[0].Value);
        r = int.Parse(B.Groups[0].Value);
    }
 }
}