Normal.
The monitor's screen display is "aligned" for the end user to be directly in front of the monitor and probably a bit to the left or right/above or below.
When I stand up in front of my ViewSonic monitor or otherwise move about its' perimeter there are all sorts of changes to colors and shading.
Happens on my All-in-one system and other monitors as well. Check you TV's. Likely the same.
Loose wire perhaps? Though looking at the specs, it is a TN panel, which has horrible viewing angles.