I had to edit these files:

/usr/share/themes/Ambiance/gtk-3.0/settings.ini
/usr/share/themes/Ambiance/gtk-3.0/gtk.css
/usr/share/themes/Ambiance/gtk-2.0/gtkrc

(Addition: for Ubuntu 12.04, it seems youjust have to modify the file: /usr/share/themes/Ambiance/gtk-2.0/gtkrc , replacing the tooltip backround and foreground color, with the #000000 and the #f5f5b5 color, respectively)

You require root privileges to edit the files. Use gksudo gedit to edit them.

Search for tooltip in these files and you'll find the color definitions for the foreground and the background. I use #000000 as foreground and #f5f5b5 as background and now the tooltips in all applications are again readable. After changing the color values simply switch to some other theme and then back to Ambiance and the tooltip color is now fixed.

vi  /usr/share/themes/Ambiance/gtk-2.0/gtkrc

tooltip_fg_color: #000000

tooltip_bg_color: #f5feb5 或 #f2edbc

Here is the result:

参考推荐：

How to change tooltip background color in Unity?

ubuntu eclipse 更改提示框背景和字体颜色

eclipse在ubuntu（12.04）中的提示面板颜色的修改

原文： Ubuntu12.04Eclipse提示框背景色修改