After some googlings, I finally found the easiest solution to fix a well known problem with Eclipse code assistant under my Linux with gnome (Mint Mate).
The problem symptom is black text written over dark gray background : simply unreadable.
To fix that, just install gnome-color-chooser, open it, go to "specifics" tab and change tooltips foreground and background colors. Restart Eclipse and enjoy!
PS : to install gnome-color-chooser
sudo apt-get install gnome-color-chooser
This tip also works on Linux Mate.