The font, font size, foreground color and background color of Tooltips in Ubuntu can be changed. This can be important since Tooltips are used by applications in Eclipse.
To change the font and the font size: Open GNOME Tweak Tool, go to Fonts section and set the font and font size for the Interface element.
To change the foreground and background colors: Open GNOME Color Chooser, go to Specific -> Tooltips and set the colors you want.
Restart your application to see the effect of these changes.
Tried with: GNOME Tweak Tool 3.10.1-2, GNOME Color Chooser 0.2.5 and Ubuntu 14.04