There are 3 screens on the N9, left the Event Screen, Mid the Application Screen and Right the Runing Programs Screen,

The Mid Screen has Black font ( i am actually not a friend of it) but it would be nice to have black fonts in Statusbar, and in all others screens;

imo i suggest White, Font, and a darker background which is about 70% sharp, making the background darker, makes it easier to read white fonts on a whrite backgrond , + the unsharp background removes ur eyes focus from the background and let you easier focus on the Foreground ( more readability)

I would also suggest making either the fonts bold in the app screen or bigger,