This nectar feeder was photographed in the forest above the farm in the Ngorongoro Conservation District. A narrow band of violet forming a collar across the breast is visible but hard to see. This is a male. Females are similar but have the throat yellow. This species may be confused with some plumages of the Variable Sunbird which has a longer, more curved bill.
HBW place this species in the genus Anthodiaeta, arguing that it has priority over Hedydipna currently used by Clements, IOC, African Bird Club and most other authors. However, see here for an alternative viewpoint.
Formerly this bird was in the genus Anthreptes, still used by Birdlife International. Nine subspecies are currently recognized, three of which occur in Tanzania. They differ in the intensity of the color of the underparts and the throat color of the females.
Reference:
Clive F Mann and Robert A Cheke. 2006. The validity of the sunbird genus Hedydipna. Bulletin of The British Ornithologists' Club 126:199-200. [HTML]
Digiscoped with Panasonic DMC-LX5 | Nikon FieldScope III | 30XWA | hand-held (no adapter).