'pigmentation' (black spots)

Hi.. i'm from singapore and i have two JRTs..
my 9mths female jack is currently on avoderm lamb and rice(not sure if this brand is familiar to you) and i've notice there's black spots.. like pigmentation on her underbelly.. and hind legs.. i've notice this a quite a common thing among the jacks in singapore.. but is there any thing.. like food or supplement that could have to lighten it?? heard that velcote and novacote can help..

my male jack that i recently adopted has this problem too.. but his 'pigmentation' is not as dark as my female jack.. he is on canine caviar chicken and rice.. he was on abady before the previous owner make the switch...

wondering if food and treats does make a difference