Comment 6 for bug 1628707

Some more information.

It seems the problem comes from the fact that the concept of a background color has been deprecated in recent versions of GTK, and no replacement has been made in the Emacs code : https://lists.gnu.org/archive/html/bug-gnu-emacs/2017-09/msg01099.html

Emacs fails to load an appropriate bg color and seems to default to this almost invisible light grey.