A gravid spot during pregnany doesn't have to turn into black. It can also tun into red, orange... you name it! A female guppy is already born with a gravid spot but not always good to see when it's still so young. This gravid spot will darken a bit till a lot depending on the base colour of the female and in what stage she's in during pregnancy. Also if the eyes of those fry will darken, the more dark the gravid spot gets. So, looking at your picture overhere, there's nothing weird about this female.
Devoted aquarist ever since early 1970's...
Specialized in livebearers &
specific breeder of rare livebearers...