Well I'm glad you enjoy a more accurate picture over the "standard" or "vivid" mode that a lot of people prefer before they're educated about industry video standards and calibration
THX mode on televisions is a mode that is pre-calibrated and accurate for a
pitch black room. And when I say pitch black, I don't just mean a normal room with the lights turned off. I mean a pitch black room where there are no light reflective surfaces and absolutely no source of light other than the TV screen itself.
Any ambient light biases the viewer's eyes. So THX mode is not 100% accurate in any normal living room. It's only truly accurate if you are also watching in a
pitch black room (and you're wearing black velvet and matte black face paint
) But that aside, THX mode typically offers far more accurate color and greyscale than the other pre-set picture modes. All you should really need to adjust are the contrast (white level), brightness (black level) and possibly the gamma if the room is on the bright side or has sunlight streaming in.
So if you're in a darkened theater, THX mode is pretty close to the industry video standards right out of the box - which is the whole idea! Some very simple and quick adjustments of the most basic user picture controls is all that's needed, which you can easily perform by eye using any THX Blu-ray or DVD and the THX Optimizer that you'll find in the disc's menu.
If you want to be really, really picky, there are still some minor unit-to-unit variations in color reproduction with any consumer television. And ambient room lighting can have a very, very minor impact on your perception of greyscale. So if you really want as close to industry spec "perfection" as possible, you still might want to bring in an ISF or THX professional calibrator, or buy yourself a good colorimeter and/or spectrophotometer and some calibration software like CalMAN or ChromaPure. But honestly, for the vast majority of people, the THX pre-set mode is "close enough" in terms of color and greyscale and some easy user adjustments to the basic contrast and brightness controls are all that's really needed to ensure you're seeing all the correct detail in the shadow and highlight areas that are dependant on your room's lighting
Enjoy!