C#

something += whatever;<br />
this.Invalidate();

public class PixelGetterHelperclass
{
	//code gotten at:
	//http://www.gotdotnet.com/Community/MessageBoard/Thread.aspx?id=330183

	[DllImport("gdi32.dll")] 
	private static extern uint GetPixel(IntPtr hDC, int XPos, int YPos); 

	[DllImport("gdi32.dll")] 
	private static extern IntPtr CreateDC(string driverName, string deviceName, string output, IntPtr lpinitData); 
       
	[DllImport("gdi32.dll")] 
	private static extern bool DeleteDC(IntPtr DC); 

	private static byte GetRValue(uint color) 
	{ 
		return (byte)color; 
	} 

	private static byte GetGValue(uint color) 
	{ 
		return ((byte)(((short)(color)) >> 8)); 
	} 

	private static byte GetBValue(uint color) 
	{ 
		return ((byte)((color)>>16)); 
	} 

	private static byte GetAValue(uint color) 
	{ 
		return ((byte)((color)>>24)); 
	} 

	public static Color GetColorFromPoint(Point p) 
	{ 
		IntPtr displayDC = CreateDC("DISPLAY", null, null, IntPtr.Zero); 
		uint colorref = GetPixel(displayDC, p.X, p.Y); 
		DeleteDC(displayDC); 
		return Color.FromArgb( 
			GetRValue(colorref), 
			GetGValue(colorref), 
			GetBValue(colorref)); 
	}  

}