The Sweetgrass are getting smaller due to the infusion of Royal Palms. The only difference in color genetics between a Sweetgrass and a Royal Palm is the Narragansett gene that Royal Palms carry. If you need to bring in fresh bloodlines to Sweetgrass, you can do so by breeding a Sweetgrass tom to Royal Palm hens. All the female offspring will be pure Sweetgrass because a Royal Palm hen cannot pass her Narragansett gene on to her female offspring. You eliminate all the male offspring because while pheontypically they will be Sweetgrass, they will all be carrying one Narragansett gene.