UI - background color in menus etc

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I tried wireshark 2.6.6 on an older ubuntu system and found its color scheme practically unusable because nearly everywhere (menus, packet data) it used very dark grey font over black background. Where does wireshark get these colors from??

I tried changing every color entry to white (ffffff) in Preferences->Advanced but nothing fixed the problem. Those variables only control colors in the window that shows 1 line / packet, and the colors there were fine in the first place. Everywhere else it is nearly black on black :/

EDIT: wireshark -v reports on that system:

Wireshark 2.6.6 (Git v2.6.6 packaged as 2.6.6-1~ubuntu14.04.0)

Copyright 1998-2019 Gerald Combs [email protected] and contributors. License GPLv2+: GNU GPL version 2 or later http://www.gnu.org/licenses/old-licenses/gpl-2.0.html This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

Compiled (64-bit) with Qt 5.2.1, with libpcap, with POSIX capabilities (Linux), with libnl 3, with GLib 2.40.2, with zlib 1.2.8, with SMI 0.4.8, with c-ares 1.10.0, with Lua 5.2.3, with GnuTLS 2.12.23, with Gcrypt 1.5.3, with MIT Kerberos, without MaxMind DB resolver, without nghttp2, with LZ4, with Snappy, with libxml2 2.9.1, with QtMultimedia, with SBC, with SpanDSP, without bcg729.

Running on Linux 3.13.0-24-generic, with Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz (with SSE4.2), with 32053 MB of physical memory, with locale en_US.UTF-8, with libpcap version 1.5.3, with GnuTLS 2.12.23, with Gcrypt 1.5.3, with zlib 1.2.8, binary plugins supported (0 loaded).

Built using gcc 4.8.4.

EDIT2: xwininfo reports:

xwininfo: Window id: 0x5a00006 "The Wireshark Network Analyzer"

Absolute upper-left X: 139 Absolute upper-left Y: 53 Relative upper-left X: 0 Relative upper-left Y: 0 Width: 1539 Height: 864 Depth: 24 Visual: 0x8a Visual Class: TrueColor Border width: 0 Class: InputOutput Colormap: 0x5a00001 (not installed) Bit Gravity State: ForgetGravity Window Gravity State: NorthWestGravity Backing Store State: NotUseful Save Under State: no Map State: IsViewable Override Redirect State: no Corners: +139+53 -242+53 -242-163 +139-163 -geometry 1539x864+136+30