Achieving a high color rendering index (CRI) and luminous stability in single-structured Ce:Y₃Al₅O₁₂ (Ce:YAG) phosphor ceramics (PCs) is crucial for high-power white light-emitting diodes or laser diodes (LEDs/LDs). However, cyan valleys and insufficient amounts of the red component in the Ce:YAG emission spectra significantly limit their real applications. In this work, a series of Ce,Mn:Y₃(Al,Sc)₂Al₃O₁₂ (Ce,Mn:YSAG) PCs were fabricated by vacuum sintering, and efficient spectral regulation was realized for full-color lighting. The cyan valley was filled by the blueshifted emission peak of Ce³⁺ via Sc³⁺ doping. The orange‒red emission at approximately 580 nm was effectively supplemented via Mn²⁺ doping. In particular, CRI of Ce,Mn:YSAG increased from 56.4 to 85.8, a 52% increase compared with that of Ce:YAG under high-power LED excitation, and the operating temperature was stable at approximately 50 °C for long working time. Moreover, CRI of 80.9 could still be obtained for PC-based white LDs. These results indicated that Ce,Mn:YSAG PC, which has excellent CRI and luminous stability, is an extremely promising color convertor for high-power white LEDs/LDs.