GTK Tooltips and Eclipse

Eclipse on Fedora (and as I read it, also on Ubuntu) has now got a problem with colors. Specifically, when one hovers over a function to obtain the calling sequence, a pop up appears to provide this information but the background of the pop-up is black, which makes the content unreadable. This is relatively new, though I’m not sure whether it was with the change to Eclipse Neon or earlier, or the change to Fedora 24.

It turns out this is not a setting in eclipse, although I wasted quite a lot of time looking for it. This ends up being a system setting, associated with gtk, the graphical toolkit. If one starts eclipse with

export SWT_GTK3=0;eclipse

which starts eclipse with gtk 2.0, instead of gtk 3.0, the problem goes away, the background of the pop-ups becomes a nice cream color.

The settings we are using are set in the theme one chooses, the default theme being Adwaita. The themes are kept in /usr/share/themes. I tried simply changing to a different theme (TraditionalOk) but the setting affecting this did not change. So I resorted to force.

In /usr/share/themes/TraditionalOk there are directories for gtk-2.0 and gtk-3.0. Within gtk-3.0 I changed the file gtk-widgets.css, specifically, I changed the setting in the tooltip section to background-color #f5f5b5; Previously the value was “@theme_tooltip_bg_color;” and as I read it, that define ought to have the value #f5f5b5. But something is wrong, and the setting is disruptd. But forcing it this way, it seems to work.