Very interesting gene. Autosomal dominant. It highlights metallic shine. It causes poliferation of melanophores – and probably that is how it influence metallic colors as well (melanophores and guanophores – responsible for shiny cover – seems to stay in strong connection, not only in case of this gene). It creates effect of pearl mass on body. So strong influence on pigment cells find his way also to fins. Magenta shortens tail fin. In heterozygotous state tail fin is small and irregular. In homozygotous form it makes usually a roundtail. Russian breeder W. Storożew mention connection between magenta gene, created by it pearl effect, melanophores and tail fin shape. In his opinion by proper selection it is possible to have magenta fish with normal, big tail fin but it has it’s price – dramatic effect of magenta will be mostly lost. Examples seems to show that the fastest way to have this effect is by using albino (affecting melanophores in opposed way to magenta, malanine is removed). Best example of coexpression of this two genes is Andrzej Konarzewski famous Polish Pink guppy. It has big fins still being a magenta.
Magenta does not have to be pink. All magic of this gene is this broad phenotipical variation. Below picture of green magenta. Breeder: W. Storożew
In general I think that magenta affects only tail fin shape. Sadly genetics of dorsal fin in guppies are not very well studied. Below you can see a splendid example that magenta can have big dorsal without being an albino. Photo owner and a breeder of a fish Kanlaya Suknipitporn.