The corolla, a collective term for all the petals of a flower, is limb and medium yellow outside and bright yellow inside for "Pachypodium bicolor". The corolla is pale green at the base, medium yellow outside with 5 very pale green lines to just below the lobes. The distinguishing character of "Pachypodium bicolor" is that its throat or the inside of the corolla tube is white for about 3.5 cm long in the mature bud. It forms a broadly ovoid head 0.3 of the bud length in comparison, measuring at . Obtuse at the apex, it is pubescent, hairy outside and glabrous, smooth on the part of the lobes covered in bud. The pubescent belt inside is wide just below the insertion of the stamens. The corolla tube is infundibuliform, or more simply funnel-shaped, at 5 to 10 times as long as the calyx—"the outer most layer of leaves in a flower, which are often green." The calyx is 1 to 1.46 times as long as the lobes at long. The basal part of the tube is almost cylindrical at 0.18–0.22 of the length of the entire tube, or long by wide. Towards the slightly widened apex, the upper part of the tube is obconical, inversely conical, at base and almost cylindrical above measuring at long to wide at the mouth. The lobe at the apex of the corolla tube are obliquely obovate at 0.6 to 0.8 times as long as the tube. That measures at 1.2 to 1.5 times as long as wide, or . The lobes are rounded at their individual apex.