What you are describing is impossible, since the camera creates the JPG file from that same raw file.
How do you know the raw file is underexposed? How are you processing it? What software, what settings? This is where the answer must lie. Check the default processing settings for the raw file in the software you are using. Go back to basics and look at the histograms.
To confirm this you could look at the raw file in Olympus Workspace, which you probably don't use, as you won't have changed its settings from the defaults.
I have not seen a bleaching problem in the viewfinder or LCD. Have you been changing the default settings for them? Or using +3 exposure compensation? Or using optical viewfinder mode, or something else?
If the dial is set to C1, C2 etc, then turning the camera off and on will revert the settings to the defaults for that stored setting.
You could reset the camera.