Voltage‐dependent, color‐tunable organic light‐emitting diodes (OLEDs) are appealing tools that can be used for the visualization of electronic output signal of sensors. Nonetheless, the literature‐reported color‐tunable OLEDs that have a simple single‐cell device structure suffer from relatively low efficiency, pronounced efficiency roll‐off, color‐aging, and short operation lifetime, all of which limit their practical applications. Here, a novel co‐host‐in‐double‐emissive‐layer (CHIDEL) device, designed to enhance the performance of color‐tunable OLEDs with the use of a single tetradentate PtO^N^C^N emitter, is described. When Pt‐X‐2 is used as a single emitter in an optimized CHIDEL device, a white OLED with tunable Commission International de I'Eclairage (CIE) coordinates from (0.47, 0.44) at 3 V to (0.36, 0.48) at 11 V, a high color rendering index of 82, and high external quantum efficiency (EQE) of up to 20.75% can be achieved. By using Pt‐X‐4 as a single emitter, the voltage‐dependent color‐tunable CHIDEL device, with CIE coordinates shifted from (0.56, 0.43) at 3 V to (0.42, 0.55) at 11 V, demonstrates a high luminance of beyond 90 000 cd m−2 and a high EQE of 23.23% at a luminance of 1300 cd m−2. A long‐lifetime time to 90% of the initial luminance (LT90) of almost 20 000 h is demonstrated for the color‐tunable OLED with Pt‐X‐4 emitting dopant. High‐performance voltage‐dependent color‐tunable organic light‐emitting diodes (OLEDs) with a single PtO^N^C^N emitter are fabricated. The emission color can be tuned from warm white to natural white or from orange to yellowish green, depending upon the emitter used. High external quantum efficiency (23.23%), low efficiency roll‐off, long‐term stability (LT90 = 19 105 h) and continuously variable color enable these color‐tunable OLEDs to find applications in smart wearable devices.