Shadow of Moil is a 4th-level necromancy spell with the following description (XGtE, p. 164):
Flame-like shadows wreathe your body until the spell ends, causing you to become heavily obscured to others. The shadows turn dim light within 10 feet of you into darkness, and bright light in the same area to dim light.
Until the spell ends, you have resistance to radiant damage. In addition, whenever a creature within 10 feet of you hits you with an attack, the shadows lash out at that creature, dealing it 2d8 necrotic damage.
The core rules state about Truesight (PHB p. 185):
A creature with truesight can, out to a specific range, see in normal and magical darkness, see invisible creatures and objects, automatically detect visual illusions and succeed on saving throws against them, and perceive the original form of a shapechanger or a creature that is transformed by magic. Furthermore, the monster can see into the Ethereal Plane.
Would a character under the effect of Shadow of Moil still have advantage against a creature with Truesight? Essentially, are "flame-like shadows" darkness, if spells do exactly what they say they do?