In a lot of applications the tooltips are just plain ugly (White text on black background, way too much contrast) or even unreadable (black or dark blue text (Hyperlinks) on black background). I want to change the background color of the tooltips to some medium gray or even some yellow or something like that, maybe even something semi-transparent.

Here is a screenshot of Eclipse which displays some source code in a tool tip with black text on black background:

Switching to a different theme (Something other than Ambiance or Radiance) helps but I like Ambiance and I want to keep it. It's just this darn tooltip color which is absolutely unacceptable.

I found several solutions for older Ubuntu versions but they no longer work with Unity in Ubuntu 11.10 because I can't find any function to customize the Ambiance or Radiance theme. So how do I do that in the current Ubuntu version?