Stella Roselaid. When performing, she does by the stage name of "Prism Pink".
Prism Lyrical (as the story is called) is a magical girl universe meant to convey a similar energy as a Saturday morning cartoon anime: bombastic, over-the-top, friendly, and ending each day with the problem solved and the cast smiling. In general, the feel and aesthetic are meant to be bright, cute, and colorful, taking inspiration from idol and magical girl anime in general and in particular, Love Live, Lapis ReLights, Pripara and Aikatsu.
It takes place in a fantasy modern day world, where magic is heavily intertwined with music and color as one all-encompassing concept that's become a societal staple. Every person's voice has its own color, and this determines what sort of magic they're able to use. While everyone is born with their color and it's easy to make a good guess as to what that color is (typically, you'll choose your voice's color as your favorite), a formal discovery isn't done until the age of nine. A test is conducted by magical experts, who are able to determine a child's color when they attempt to manipulate a certain type of magical crystal and see how it glows. A person's color can exist anywhere on the color spectrum, and can be tested down to the exact shade, though minor differences between shades rarely make a difference in a person's capabilities. Certain colors of magic may exist in stronger quantities in some places than others, but because most people's magic use is limited to basic tasks and a few party tricks, the fact has few practical effects.
One major exception exists: a 100% pure shade of one of the visible spectrum's base colors—red, orange, yellow, green, blue, indigo, or violet—is referred to as a Pure Perfect Color. White also exists, technically, as a combination of the other seven at once, but only one recorded instance of a Pure Perfect White exists, and there are doubts the phenomenon could occur again. Even compared to any specific minor off-color shade, a Pure Perfect Color voice is incredibly rare. It's also wildly valuable. A young girl with a Pure Perfect Color voice, instead of relying on environmental magic, can create magic of her color and usually has a strong affinity for a certain type of magic that she can use with much more power and much more precision that the general population. For instance, Citrine Thunders, the current Pure Perfect Yellow has lightning elemental magic, while Celeste Charleston, the current Pure Perfect Blue, has powers relating to manipulation of gravity. Because of this, Prism Maidens will sometimes have their colour identified earlier in life than is typical, depending on how showy her magic is, but it's not uncommon for her colour to go undiscovered until later in life.
Upon discovery of a Pure Perfect Voice, the girl holding it will immediately be given the opportunity to become a Prism Maiden. As magic and music are so heavily intertwined, the Prism Maidens function essentially as a group of idols, similar to Japanese entertainers of the same name. Using a magic crystal called a Vertex Stone, they channel magic to "transform" (as any good magical girl does) through a magic costume change into their idol outfit. A Vertex Stone is simply a crystalline conduit through which they can cast some of their magic; the Vertex Stone takes the form of a different accessory for each girl, such as a pendant or an earring. They sing, dance, and use flashy magical effects in their shows. This use and creation of magic has a practical purpose: each girl generates magic of their color as they perform, releasing it into the world to be used by others. Creation of colorful magic also aids in the fight against the Drone.
If all magic has a color, then the Drone is dull gray. Colorless, it trawls through the world and saps the color from the world around it. Less a living, breathing thing and more a force of nature, it wants only to take the color and magic out of the world, leaving a monotonous hum behind. By creating magic, the Prism Maidens can repair damage caused by the Drone, but they also use magic and color to overwhelm it and drive it back. Without their timely intervention, the Drone can throw out the balance of an environment's color energy, which affects different things in different ways depending on the color and the color affinities of the people there. Depending on the sort of imbalance, and the magical affinities of the Prism Maidens this can be either a bit uncomfortable or very dangerous – an imbalance of Yellow might lead to localized electricity storms for example.
This, at least, is easily fixable, and doesn't have long-term ramifications if taken care of swiftly, despite being potentially dangerous in the moment. However, if not stopped in time, the Drone can drain away all the color from an environment. Magic is energy and a part of all people; needless to say, loss of all color is a worst-case scenario for all involved. Because of this, the Prism Maidens serve an important role in keeping the world balanced and safe.
As of the time of the story, the current group of Prism Maidens is in something of a pickle: due to the rarity of Pure Perfect Colors, the group is incomplete and missing representatives from a few parts of the color spectrum. This inhibits their ability to keep magic balanced and whole. As such, they're in something of a frenzy to track down missing members.