Monitors, televisions, and smartphones have been revolutionized by the invention of InGaN-based LED backlighting. Yet, regular exposure to the bright blue light emitted by these screens can lead to mood disorders and insomnia. Switching to a "human-centric" display that uses a violet-emitting LED chip and a trichromatic phosphor blend is one materials chemistry solution for this problem. The challenge is finding a blue-emitting phosphor with a sufficiently small Stokes’ shift to down-convert the violet LED light. This study reports a new oxynitride phosphor that meets this need. K3AlP3O9N:Eu2+ exhibits a narrow (45 nm, 2206 cm-1), thermally robust, and efficient blue photoluminescence upon violet excitation. Computational modeling and photoluminescence spectroscopy revealed that a rare combination of preferential excitation and site-selective quenching produce the desired optical properties. Combining K3AlP3O9N:Eu2+ with red- and green-emitting phosphors and a violet LED covers 10% more of the color gamut than a commercial tablet while simultaneously mitigating blue light exposure en route to next-generation, human-centric displays.