Sorry I missed your post Armand!

The best method is collection info. Visually, in maps, there is very little, to absent all together row of iridecent spangling under the dorsal fin and no spotting on the flanks. leuco's always have this line under the dorsal no matter what level of spangling on the flanks. Also, maps have broader snout, small to medium tightly packed spots on the muzzle. From my research the color of the spotting on maps is consistently more green and blue that just blue alone.