Keep this in mind, gams are live bearers. So, unless you know the daddy of each baby growing in the belly of each pregnant female was also golden you're gonna end up with the wild color form in the population. It would be real tough to guarantee that you knew the lineage of each father gam.

I used to breed the spotted black form as a kid. I caught them from the wild and selectively bred them until I had all black males and nearly all black females. It was an interesting hobby. Guppies, who needs guppies!