In another forum on Mobileread the Onyx rep states that the screen is Pearl. Pearl appears to be a descriptive term used by Vizplex rather than a trademarked brand.
This site states that it is a Vizplex PEARL with 50% higher contrast than standard e-ink. Given that standard e-ink is 6-7:1 I am not sure how that equates to the 12:1 figure I have seen floating around. But I do get the feeling that the m90 has the Pearl screen. At the very least it means that it is higher than standard e-ink screens but I am not 100% sure it means the 12:1 ration expected of the pearl best screens.