code: def sortkey(x):
      
      r = x[1] / 255.
      g = x[2] / 255.
      b = x[3] / 255.
      cmax = max(r, g, b)
      V = str(int(round(cmax * 100))).zfill(3)
      cmin = min(r, g, b)
      delta = cmax - cmin
      if delta == 0:
          hue = 0
      elif cmax == r:
          hue = 60. * (((g - b)/delta) % 6)
      elif cmax == g:
          hue = 60. * (((b - r)/delta) + 2)
      else:
          hue = 60. * (((r - g)/delta) + 4)
          
      H = str(int(round(hue))).zfill(3)
      
      if cmax == 0:
          sat = 0
      else:
          sat = delta / cmax
      S = str(int(round(sat  * 100))).zfill(3)
  
      return H + S + V
docs: Return Hue, Saturation, Value string for (colorname, r, g, b).