How to change tooltip background color in Unity?

Install and open gnome-color-chooser .

Go to Specific → Tooltips and put black foreground over pale yellow background.

Found it!

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.

Here is the result:

If you want to change the tooltip colors for all apps then install and run gnome-color-chooser and go to Specific tab > Tooltips. Check the boxes for Foreground and Background and choose colors.

How it works (you can do this manually):

gnome-color-chooser adds the following to your ~/.gtkrc-2.0:

include ".gtkrc-2.0-gnome-color-chooser"

and ~/.gtkrc-2.0-gnome-chooser:

style "gnome-color-chooser-tooltips"
{
  bg[NORMAL] = "#FFFFAF"
  fg[NORMAL] = "#000000"
}
widget "gtk-tooltip*" style "gnome-color-chooser-tooltips"

If you just want to change the tooltip colors for a single app, such as eclipse, then put the above text into a custom gtkrc file (e.g. ~/gtkrc-eclipse) and start eclipse with GTK2_RC_FILES=~/gtkrc-eclipse eclipse

I created a small script that does that for you

#/bin/sh
# Tooltip fix
# A script to fix themes files in Ubuntu 11.10
#  to have readable tooltips in applications such
#  as eclipse.
# The script edits the gtk.css, settings.ini and gtkrc files
# Author: Victor Pillac
# http://victorpillac.wordpress.com

if [[ $EUID -ne 0 ]]; then
  echo "This script must be run as root" 1>&2
  exit 1
fi  

path=/usr/share/themes
theme=Ambiance

if [ $# = 1 ]; then
  theme=$1
fi

echo "Fixing tooltips for theme $theme"
echo " (you can select a different theme by passing its name as argument)"
sed -i 's/tooltip_bg_color #000000/tooltip_bg_color #f5f5b5/g' $path/$theme/gtk-3.0/gtk.css
sed -i 's/tooltip_fg_color #ffffff/tooltip_fg_color #000000/g' $path/$theme/gtk-3.0/gtk.css
sed -i 's/tooltip_bg_color:#000000/tooltip_bg_color:#f5f5b5/g' $path/$theme/gtk-3.0/settings.ini
sed -i 's/tooltip_fg_color:#ffffff/tooltip_fg_color:#000000/g' $path/$theme/gtk-3.0/settings.ini
sed -i 's/tooltip_bg_color:#000000/tooltip_bg_color:#f5f5b5/g' $path/$theme/gtk-2.0/gtkrc
sed -i 's/tooltip_fg_color:#ffffff/tooltip_fg_color:#000000/g' $path/$theme/gtk-2.0/gtkrc
echo "Done"