since that annoyed me all the time since i got my n900, and since i don't see any solution to this annoying problem, i'd like to share with you what i found out in the depths of the interwebs:

https://bugs.maemo.org/show_bug.cgi?id=7127#c13

this really works fine for me, and i'm really really really thankfull that my eyes got not distracted by a bunch of colored pixels