C#

Color bgColor = Color.Black;
g.FillRectangle(new SolidBrush(bgColor), 0, 0, this.Width, this.Height);

int val = bgColor.ToArgb();
val  = ~val; // Negate bg color
Color foreColor = Color.FromArgb((0x000000FF & (val >> 16)), (0x000000FF & (val >> 8)) , (0x000000FF & (val))); // Split and give R,G and B components.

g.FillRectangle(new SolidBrush(foreColor), 0, 0, 100, 100);

class Test
{
   int val = 0;
   AutoResetEvent evt = new AutoResetEvent(false);

   void MainThread()
   {
      new Thread(new ThreadStart(ThreadFunc)).Start();
      // Do some work
      // We need value of val to proceed
      evt.WaitOne(); // Wait till thread completes.
      Console.WriteLine(val);
   }
   
   void ThreadFunc()
   {
      Thread.Sleep(2000);
      val = 1000;
      evt.Set(); // Signal to main thread
   }
}