A sweetgrass is a Royal palm without the Narragansett genes. A fall fire is a sweetgrass with a songle red gene.
Royal Palm = b1b1cgcgngngRR (b1 = black wing based, cg = gray gene, ng = narragansett gene, and R = not red gene), more commonly written b1b1cgcgngng
Sweetgrass is b1b1cgcgNgGNgRR, where Ng= "not narragansett", also written b1b1cgcg.
Fall Fire = b1b1cgcgNgNgRr, or b1b1cgcgRr.
The lack of reddish tint in the overtail coverts has me leaning towards sweetgrass, although the shoulder is dark. The Royal Palm quality of the chest is surprisingly well preserved.
Any clue as to what the parents looked like (so we could deduce whether ot not a red gene is present)? The parents may have looked nothing like sweetgrass or royal palm.