Fischer's Lovebirds (discovered and named after Gustav Fischer in the 19th century) are a species of lovebirds native to Tanzania, Africa. They are smaller than peachfaces and do not have as many recognized color mutations.
The average Fischer is green on the chest, back, and wings, with a gold neck that gradually darkens to orange as the coloring reaches the bird's face. The tops of their heads are dusky green, their rumps are blue, and their beaks are red. Unlike the peachfaces, Fischers have a thin ring of bare skin around their eyes.
Fischers are the one of the smaller species of lovebirds, averaging about five and a half inches, and while they do chatter, their voices aren't as shrill as those of other lovebird species. Like all lovebirds, they're active budgies that like playing with and destroying bird toys, escaping form their cages, and chewing things. They are regarded as one of the most friendly and playful species of lovebirds, but like with all pets that depends on how much effort you put into the relationship.
Like peachfaces, Fischers have a green-series and a blue-series, and are susceptible to the lutino, dark factor, cinnamon, fallow, violet, and pied mutations. As with peachfaces, each mutation presents itself in two variations depending on whether or not the bird is green-series or blue-series. Blue muties have blues instead of greens, and grays/whites instead of yellows/oranges.
While in general these mutations are presented very much like those of the peachfaced variety, there are still subtle differences due to the way pigmentation is set up in each species (such as the lutino's having a slightly more orange coloration, and that coloration enveloping the entirety of the Fischer's head, rather than just it's face). They also have their own mutation called "spangled" (or "edged" for you folks outside of the States) wherein the wings have colored bands.
Unlike the peachfaces, it is possible to have an albino Fischer lovebird, though some breeders may get persnickety about this because the only reason a Fischer is capable of having albinism (and lutinoism, for that matter) is because somewhere down the line there was a Nyasa lovebird bred in, meaning that the resultant family line of Fischers aren't pure Fischers, and hybridization is typically frowned upon with lovebird breeders.
A double dark factor in a Fischer is called an olive, a single dark factor is usually called a pastel-olive. Cobalts are the single dark factors in a blue-series, and mauves are double-dark factors.
Fischers can be successfully bred with any of the other three eye-ring lovebirds: Nyasa, Masked, and Black-Cheeked. While it is possible for eye-ringed lovebirds to breed with lovebird species without the rings, it is highly frowned upon because not only are the babies infertile, but they are susceptible to major health issues.