LCD is normally brighter.
As for dull color, I am not sure if you have checked your white balance setting?
Maybe you want to calibrate your camera's white balance.
As for f-stop, there are a lot of factors you will need to consider when you set.
Setting wide open aperture can allow more light to come in. If you are setting f/2.8, the DOF will be shallow. If you are setting F/8 to f/11, the you will have a good DOF.
Hence, there is no right or wrong setting. It depends on what you want to achieve.
Giving an example, you are taking an old man's photo in Tibet, and the old man is leaning against a big wall. Do you need to set f/2.8 to achieve bokeh/shallow DOF? Chances are not, right?
Try the calibration of your camera's white balance setting, coupled with a CP filter, and the suggestion given above, go and make another attempts, maybe, the result will be more satisfactory.