Organic light-emitting diodes (OLEDs) are a key technology in solid state lighting. Without a long-lived phosphorescent blue emitter, a hybrid concept based on phosphorescent red and green emitters and a fluorescent blue emitter in a white OLED stack is a promising approach for pure-white emission. Several challenges such as exciton recombination on all emitters and triplet diffusion, as well as quenching, have to be overcome. To address these issues, a mixed-host phosphorescent emission layer is employed. The mixture ratio is locally varied in the emission layer. An interlayer separates the phosphorescent and fluorescent emission layer. Strategies to tune the color coordinates are presented. The lifetime and color stability versus luminance are investigated. At Commission Internationale de I’Eclairage color coordinates of 0.44/0.44, a current efficacy of 28.0 cd/A (at 1000 cd/m2), and a luminous efficacy of 20.6 lm/W can be measured.