using System;
using System.Runtime.InteropServices;
 
namespace ChooseColor
{
    class Program
    {
        [StructLayout(LayoutKind.Sequential)]
        public struct CHOOSECOLOR
        {
            public Int32 lStructSize;
            public Int32 hwndOwner;
            public Int32 hInstance;
            public Int32 rgbResult;
            public IntPtr lpCustColors;
            public Int32 Flags;
            public Int32 lCustData;
            public Int32 lpfnHook;
            public Int32 lpTemplateName;
        }
 
        static void Main(string[] args)
        {
            CHOOSECOLOR choosecolor = new CHOOSECOLOR();
 
            choosecolor.lStructSize = Marshal.SizeOf(choosecolor);
            choosecolor.hwndOwner = 0; //GetDesktopWindow();
            choosecolor.rgbResult = 0x808080;
            choosecolor.lpCustColors = Marshal.AllocCoTaskMem(64);
            choosecolor.Flags = 3;
 
            ChooseColorA(ref choosecolor);
            //get the color from rgbResult member
       }
 
        [DllImport("comdlg32.dll")]
        public static extern int 
            ChooseColorA(ref CHOOSECOLOR pChoosecolor);
 
        [DllImport("user32.dll")]
        public static extern int GetDesktopWindow();
    }
}