It's
amphiacanthoides. My orange usually did show a peach-colored belly at a small size. It spread into their entire chest as they grew.
It used to be said that the black triangular blotch on the orange Uaru didn't reach all the way to the caudal peduncle, while it did on the typical amphs. If you go look at the recent pictures from Jeff Rapps of the adult Uaru he imported from Rio Tapajos, their blotch stops short of the caudal peduncle and they have a more orange appearance. So either Rio Tapajos is the origin of U. sp. 'orange' or there are multiple sources of fish showing similar characteristics.