Ask HN: Do darker pixels use less power?

I am asking because it seems to me that the closer a pixel on an LCD monitor is to off, the less power it should take to display it. If so, sites that are commonly used as homepages and/or just visited often (e.g. google, facebook), could reduce the energy usage of client machines by using a large percentage of darker pixels (e.g. black background, lighter text). Considering the amount of client monitors displaying those sites on a daily basis, couldn't this make a significant difference? background-color: #000; FTW?!