Comment 3 for bug 1515829

A work around to this problem is explained in the following link:
http://www.iwillfolo.com/how-to-change-gtk-apps-tooltips-text-and-background-color/

The problem seems to be some incompatibility as explained in that page, as per quote below:
"When utilizing a desktop environment other than GNOME, or when using a non-default theme in GNOME-shell itself, you may often encounter incompatibilities which are mostly reflected through native GTK apps such as GIMP, Nautilus, Totem, etc…"

The solution explained there about modifying file "~/.gtkrc-2.0" worked for me.