The red-bellied parrot (Poicephalus rufiventris) is a small African parrot about 23 cm (9 in) long of the Poicephalus genus. Some guidebooks call this the “African Orange-bellied Parrot” so be sure you check the scientific name. It is a mostly greenish and grey parrot. Males have a bright orange belly and females have a greenish belly.
I saw them in two different locations at Tarangire, one in the small Serengeti plain and one near the campground. Here’s a close-up of the male & female respectively, then some photos showing their environment.
It was a challenge to find a video of these birds in the wild but here’s one.