A distinctive feature of this species is the extremely high-arched, spherical and smooth dorsal carapace with the eponymous yellowish lines radiating outward on each carapace segment on a dark background. In most rayed turtles, the base color of the carapace is lacquer black with characteristic yellow stripes emanating from a light center. The reverse color variation with a light yellow background and black radial stripes is less common. The ray pattern, which is individual for each specimen, continues on the dorsal carapace as well as on the ventral carapace. The basic color of the plastron is yellow and shows a pattern with black areas and lines.
In young specimens, the ray markings are usually particularly colorful and distinct. With age, the characteristic pattern increasingly fades and due to wear (rubbing against stones and bushes) the concentric growth rings of the carapace are usually no longer recognizable. Very old specimens may therefore be completely washed out yellow or black. A distinction is made between dark and light individuals based on the amount of yellow present. Particularly conspicuous and popular are ray turtles, which have a clear, uniform, yellow ray markings pronounced on all shields. These specimens are also referred to as "High Yellow". Animals that are completely devoid of markings and are completely black are rare. Although the yellow and black line pattern may appear conspicuous at first glance, the outlines of a resting ray tortoise completely dissolve in a dry grass or scrub environment. Hatchlings of Astrochelys radiata still possess an inconspicuous baby camouflage pattern in their first year of life. This makes them particularly well protected from predators on sandy, stony soils and in dry foliage. The characteristic ray pattern becomes visible only with the appearance of the first growth rings, after about 1 ½ years.
The top of the head is ash colored and may have several light spots, the throat and neck are cream to yellow. The very stout legs and tail also have a yellow coloration. The horn scales of the forelegs are round and flat. The claws are conical and rather blunt. Unlike its sister species, the Malagasy Ploughshare Tortoise, it does not have a prominent extension of the gular shield at the anterior end of the ventral carapace. The posterior marginal shields are somewhat curved up and serrated, and the caudal shield is undivided and curved downward. The ventral carapace is yellow with a large black triangle on the outer edge of each of the arm, thoracic, ventral, and thigh shields. The throat shields are mostly featureless. The anal shields and sometimes the ventral shields have black ray markings. A nuchal shield is present, the supracaudal shield is undivided, and there are 11 marginal shields on each side of the carapace.