if( GUI.Box( rect, firstBoxTexture ) )
{
   // Drag
   if( firstBoxTexture != null )
   {
      currentTexture = firstBoxTexture;
      firstBoxTexture = null;
   }
   // Drop
   else
   {
      firstBoxTexture = currentTexture ;
      currentTexture = null;
   }
}

what kind of condition i will put if needed the firstboxtexture=yellow then my 2nd boxtexture=white when i drag the firstbox=yellow to the 2ndbox=white the 2ndbox will change to yellowbox and if its wrong the scene will restart..