this is indeed fro the hypo line amyae from Steve.
hypo-melanistic (means; reduction of black coloration) is a linebred-trait ; so created by selctive breeding over several generations .
amelanistic is a recessive trait like albino and patternless.
there is nothing you van do to increase the possibilityof a new recessive trait, you just need to be very lucky!
so Bjorn if you want to breed a hypo to your line thats possible .
lets say it this way ; if you breed the best hypo to a normal annimal you will get babies that are somewhere in between in coloration(black pigment).
but you can also have a peak up (a hypo) or a peak down (a normal)
the best/fastes way to get a hypo is then off course hypo X hypo , but it is possible to breed to a normal only that takes more time(several generation probably) to get a hypo.
you say some annimals already lack of black pigment so your half way trough!!
i hope this clears up the sky
@Tony , this is a female

, but indeed with very litle black pigment left and she is about 16 grams and they color up til sexually mature , so she will probably become even nicer.
i will make an update intime.