There are three main types of panels used for TV/monitors: TN, VA and IPS.
IPS has the widest viewing angles, TN has the worst and VA is in the middle. However, VA has the greatest contrast ratio of the three.
When you view a TN or VA pannel at angles outside the sweet spot, you get color shift and reduced saturation.
If your TV is based on a VA panel, then the dull image would be normal. Adjust your TV's tilt to point down until the sweet spot is where you normally watch from. If your wall mount doesn't do tilt or not enough of it, then you may need a different mount or need to adjust it some other way.