The 12" PB is perhaps better thought of as a "super-iBook", which is to say that it doesn't have the greatest LCD (at least, not the quality of LCD that you'd expect in a PowerBook.)
That said, download SuperCal from versiontracker.com and see what that does for your personal satisfaction level. As far as contrast goes, I just use the Display Sytem Pref, and set my color profile to sRGB. My SuperCal profile was remarkably close to that setting.