code: def normalize_rgb(r, g, b, a):
      
      r = int(r, 10)
      g = int(g, 10)
      b = int(b, 10)
      if a:
          a = float(a) * 256
      if r > 255 or g > 255 or b > 255 or (a and a > 255):
          return None
      color = '#%02x%02x%02x' % (r, g, b)
      if a:
          color += '%02x' % int(a)
      return color
docs: Transform a rgb[a] color to #hex[a].