input: Write a python function to separate objects into two groups based on their color property.
  assert separate_objects([Obj('red'), Obj('blue'), Obj('red')])==([Obj('red'), Obj('red')], [Obj('blue')])
  assert separate_objects([Obj('blue'), Obj('blue'), Obj('red')])==([Obj('red')], [Obj('blue'), Obj('blue')])
  assert separate_objects([Obj('red'), Obj('red'), Obj('red')])==([Obj('red'), Obj('red'), Obj('red')], [])
output: def separate_objects(objects):
      red_objects = [obj for obj in objects if obj.color == 'red']
      non_red_objects = [obj for obj in objects if obj.color != 'red']
      return (red_objects, non_red_objects)