Hello. These monitors are known to have mediocre color settings.
First, try setting up the settings in the monitor menu to this:
Mode - photo
Brightness 100
Contrast 58
R88 G92 B84
Sharpness max
Digital v. 100
Some people have had good results with this setting.
If there is no change, then you can always change your color profile. The procedure for this is found here:
https://www.youtube.com/watch?v=B63Y6QyVzyw
As for the stretching, please check and confirm your game runs at 1080p, the correct resolution for this monitor. If it runs at a lower resolution, black bars or the like are possible.