You have no idea what X is. You think 4 looks nice, but it could be anything.
The panel doesn't know what the right answer is. The display controller might see it in the signal, but it can't send that information to the panel if it's processing 6 bpp.
For 6-bit panels, you simply can't do anything to recover the signal in any correct way. Interpolation doesn't do anything but make everything look worse. Temporal interpolation is fucking terrible, and no, it's not "way faster than the human eye can tell". Most panels have a hard enough time with ghosting and motion blur already, even when adding timed strobing to the mix.
I don't think gamers are the ones who are concerned with color accuracy - gamers tend to buy the TN or other trash panels that absolutely fuck color in favor of speed. As for sub millisecond color changes? Please show me an LCD panel with a true response time under 1 ms. As for 1.5% color changes, that's a huge difference for anyone with normal color vision. A good panel will show this difference quite readily. http://i.imgur.com/w8qQ7Kg.gif for an example. If you can't see it flashing, get a better monitor or get your eyes checked.