DIAGNOSIS This is color uniformity variance, often called "IPS glow" or backlight bleed. A slight tint on the edges, particularly in dark content, is a characteristic of Nano IPS panels like the one in the 27GP850-B.
FIX First, ensure your viewing environment and angle are correct. Sit directly centered in front of the monitor. The tint is most visible from an angle. Adjust the monitor's tilt and height so your eyes are level with the center of the screen. Next, adjust the monitor's brightness. OSD > Picture > Brightness. Lower it from a default 100 to between 60-80 for typical room lighting. High brightness exacerbates glow. Finally, in the OSD under Picture, set Gamma to Mode 2. This is the most accurate gamma and can improve shadow detail, making the tint less noticeable.
IF THAT DIDN'T WORK The tint could be influenced by the color temperature setting. In the OSD under Picture > Color Temp, try switching from Cool or Custom to Warm. This reduces blue light, which can minimize a perceived purple cast. For a green tint, manually adjust the Custom color temp, reducing the Green gain slightly.
HEADS UP True backlight bleed appears as cloudy white/yellow patches, not a uniform tint. IPS glow is normal and appears as a purplish, bluish, or golden glow that shifts as you move your head. It is not a defect unless it is severe and obstructs content in a well-lit room. Photographing it often makes it look worse than it appears to the eye.