The description for Chromatic Orb states (PHB, p. 221):
You hurl a 4-inch-diameter sphere of energy at a creature that you can see within range. You choose acid, cold, fire, lightning, poison, or thunder for the type of orb you create, and then make a ranged spell attack against the target. If the attack hits, the creature takes 3d8 damage of the type you chose.
However, it doesn't mention any saving throw details. My understanding is that the only risk with using a ranged spell is that if you're within 5 feet, then you will cast the spell at disadvantage (PHB 195). However, the description of Chromatic Orb clearly includes the words "If the attack hits." Nothing is stated for the conditions in which the ranged spell attack could miss, such as a successful saving throw. So, how could this spell ever not hit the target?