Diagnosis
The color calibration is off. This is usually due to the mixed-color LEDs (RGB) aging at slightly different rates or a firmware rendering issue, not immediate failure.
How to Fix It
First, update the bulb's firmware via the Tapo app. Then, perform a manual color recalibration. In the app color picker, cycle the bulb to pure white, then to solid red, green, and blue. Use the color wheel to select a known hue (like sky blue #87CEEB) and check output.
If That Didn't Work
The problem may be physical. LEDs degrade with heat. If the bulb has been used for thousands of hours at high brightness, one color channel (often green) may be dimmer. This requires bulb replacement.
Heads Up
Perceived color is highly dependent on the surrounding environment and other light sources. Test the bulb in a dark room alone for accurate assessment.