code: def colordiff(rgb1, rgb2):
      
      (r, g, b) = rgb1
      (r2, g2, b2) = rgb2
      return (
          max(r, r2) - min(r, r2) +
          max(g, g2) - min(g, g2) +
          max(b, b2) - min(b, b2)
      )
docs: From w3c (greater than 500 is good).
         (range [0..765])