If the OS can boosting to 24bits or 32bits even better, then those blocks will be less. Linux can do that too, not just windows, changing graphic depth is all depending on the graphic driver. But why on earth didn't NOKIA by default set it to 24bits or 32bits?
Take a look at a black and white!! Will you say black and white screen a good quality screen? The screen can be good but there is the colour is not real then it is not a quality screen.