How you know that the LCD is using 6 or 8 bit / color panel? The hard one is by searching what panel the are use and than you search the detail spek of that panel. The easy one? Just check the color the support. The LCD that using 6 bits / color are only support a marketing number of 16.2 million colors. The 8 bits / color LCD are support color 16.7 million.
If you using 6 bits / color, meaning you have 18 bit all color. That mean your LCD is emulating 24 bit color using 18 bit color. It is like interpolating color. Why we must be cheated? So when you buy LCD plese check the maximum supported color wheader it is 16.2 million or 16.7 million color. And please choose the 16.7 if you are not like to be cheated by LCD company.
I hate when marketting doing this. The calculation of 18 bit is 262K color. Using interpolation the marketing can jump the color from 262K to a whopping 16.2 million colors. I almost miss the desimal point. Before I know this, I think what else color support 24 bit beside 16.7 million color? It turn out that there are 16.2 million color beside 16.7 million color.
Almost all LG using 16.2 million color. Dell beside Ultrasharp series is also using 16.2 million color. Samsung is balance just check the color, I thing the TOC series if free from 16.2 million color. Many low end model like VA from ViewSonic, Acer, Asus, BenQ are just using 16.2 million color. If you want to know the exact model, try searching with this keyword: LCD Company + color + 16.2 million in Google Product. I bet there are many result come in.
Well good luck with choosing the right LCD :).