Panu, it's real subjective, but in my opinion, for clarity, nothing beats #FFFFFF on #000000.
(Black on White)
However, when you invert it, it can be too intense for many folks, and I usually go for #222222 on #eaeaea, which I find to be very readable.
What you want to avoid is colors on opposite sides of the
color wheel with similar brightness values.
The worst thing about much of SONAR's UI is the lack of contrast - color values where foreground and background have similar brightness levels (mostly mid-levels).
This post probably wasn't helpful.